The early Marvel comics averted Comic-Book Time hard and allowed stories to flourish in almost Real Time and have characters age, progress and change. Gradually, brakes were applied and the concept, initially referred to as "Marvel time" was first introduced in 1968 in the letters' pages of the Fantastic Four comic. A reader asked about the time that passes between comics, as it would not be consistent. Stan Lee replied "Although a complete story may take place within a day, that doesn’t necessarily mean the next story takes place the very next day. The following yarn could begin the next day, the next week, the next month, or even the next year". Marvel's official stance is that the modern Marvel era began with the space flight that gave the FF their powers, and that at most about 14 in-universe years, give or take has passed and that includes the entire Shared Universe across all titles, and that means all adventures past, present and future will have to transpire in the same 14 years.
It has been suggested that Marvel's timescale works at a rate of “four years in the real world equals one year for the Marvel Universe”. Based on this and the start of the sliding timescale being the Fantastic Four's launch, approximately 15.5 years has passed since then to now.
Avengers: Earth's Mightiest Heroes (2005) adds modernized, behind the scenes details to the early The Avengers stories that did not exist during the '60s, such as Captain America visiting the Vietnam War Memorial.
Avengers: The Origin attempts to streamline the early Avengers stories into the vaguely recent past, where Rick Jones and the Teen Brigade are using flatscreen computers instead of ham radios. The members of the Teen Brigade are also more racially diverse than in the 1960s, when the group was mostly depicted as a group of white kids.
Pretty much everyone, but most especially Reed and Sue's son Franklin, who was born in 1968 and yet didn't reach puberty until 2018, and even that was only due to the multiversal Time Skip the FF characters underwent following their disappearance at the end of Secret Wars (2015).
This is especially underscored by the original FF backstory, which had Reed and the team conducting a test flight of his experimental spaceship because they considered it urgent that America put humans into space before "the commies" (Sue's exact words). A late '90s FF annual by Karl Kesel and Stuart Immomen lampshaded this when the 616 Ben Grimm got transported to a parallel Earth where the Silver Age Marvel Universe had aged in real time. The Thing was horrified by the 1961 origin date of that world's FF, realizing it's likely his counterpart was a WWII veteran.
Of course, in the real world, there's no "likely" about it: both Ben and Reed were explicitly identified as vets early on in the comic. Reed was an intelligence officer in Europe (who even guest-starred in an issue of Sgt. Fury and his Howling Commandos) and Ben was a Marine pilot in the Pacific.
Likewise, a storyline in The Invaders revealed that as a young man, Victor Von Doom had briefly worked as a scientist for Adolf Hitler under the assumed name "Hans." After sabotaging an experiment meant to bring Asgardian trolls to Earth, Doom expressed his disgust towards Hitler (particularly since the Nazis had targeted the Romani people, an ethnic group Doom belongs to), but chose to leave without killing him. A later story in the 90s smoothed out the timeline inconsistencies by revealing that rather than being a young Doom, Hans was actually the present day Doctor Doom (or rather, the Silver Age Doom), who'd used a time machine to travel back to the 1940s in order to study the Nazis during their last days. He also admitted that he'd wanted to kill Hitler right then and there, and only spared him after remembering that Hitler was already destined to die soon after in the closing days of the war.
The Tales of the Marvel Universe one-shot published in the wake of Onslaught has a scene where a cab driver recalls having given a ride to Sue back when the team was still operating out of Central City, which would've been during the very early issues of the Lee/Kirby run. The cabbie says the encounter must've taken place around ten years ago, even though it was more than 35 in real world time.
Spider-Man started superheroing in 1962 when he was 15 (Which means that Peter Parker is as old as George W. Bush in real-time), and real-time aging was practiced in the original run allowing him to graduate from high school in Issue 28 and go to college. His aging slowed after that, taking more than 120 issues before he graduated from college, after which he went to grad school, where he has remained to the present day. As per the mandate of the Post-OMD Cosmic Retcon, Spider-Man in the 616 Continuity is in his mid-20s (between 24-27) and at most 14 years have passed in Spider-Man's continuity, and that's the most Spider-Man will ever be allowed to age, with Dan Slott noting that Marvel editorial will never allow Spider-Man to hit his '30s.
Particularly striking in a 2016 storyline where Peter and Silk time-travel back to the day of the radioactive spider bite, which is explicitly said to take place in 2006. Not only does that mean modern-day Peter is now 25, it's hard to believe that all of Spidey's adventures fit into just a decade. Even more confusingly, at one point in the comic Peter says that they can't use Google since they're in the past. Google has been around since 1997 and was the largest search engine by 2000. And the Pete of 2006 still dresses like it's the sixties.
The first issue of Kurt Busiek's The Marvels has a flashback to 12 years ago, and Flash Thompson is shown to already be in the army. This would make him, and, by extension, Peter, at least 30 years old (or maybe 29 if Flash graduated high school at 17 and the flashback took place very shortly after his enlistment, but even that’s a stretch). However, due to the writers not wanting to make the character seem too old, Peter is perpetually stuck somewhere in his 20s.
The comic Spider-Girl started in the late 1990s in a version of the Marvel Universe without Comic-Book Time; Spider-Man was in his 40s, and had a daughter with Mary Jane Watson, the titular Spider-Girl. Of course, after the book started, Comic-Book Time kicked in; it's been about ten years, and she's moved from a sophomore to a junior in that time. The 2008 Mini SeriesGeNext does the same real-time gimmick and stars the kids and grandkids of the X-Men. (Though in this case they're the grandkids specifically of the versions seen in the also AU X-Men: The End)
Ultimate Spider-Man, is an AU where Marvel deliberately experimented with a high school Peter Parker who never ages passing 200 issues without him and his cast leaving high school. Eventually Peter was allowed to age a little bit, during his "death" and "return", where a second teenage Spider-Man, Miles Morales took over. When Ultimate Peter returned he had aged from 15 to 18 before the series wrapped up.
Spider-Man: Life Story by Chip Zdarsky is an AU that explores how Spider-Man's world would have looked like had he aged in real time from The '60s to The New '10s. The first issue clarifies that the original L-D Era (which had real-time aging) is canon, but every run after that is altered and twisted to allow characters to age and progress. This also applies to the rest of the Marvel Universe, as the series' take on Civil War depicts many of the heroes involved (like Iron Man, Captain America, Luke Cage and Hawkeye) with gray hair and wrinkles. The series ultimately ends in 2019, with an elderly Peter dying and the Spider-Man mantle officially passing to Miles Morales.
Kitty "Shadowcat" Pryde was introduced during the '80s as a thirteen year old girl. Character Development saw her grow from an inexperienced kid into a full member of the team, go through numerous names, develop as an electronic whiz, psychically learn a lifetime of ninja skills, become a founding member of the British based superhero team Excalibur, and work as an agent of S.H.I.E.L.D.... Yet she takes a break from being a superhero to go to college full time.
Special mention must go to how her first romantic relationship with team member Colossus was aborted due to the fairly wide gap in their ages. Twenty years of real time later, when Colossus comes Back from the Dead (long story), Kitty has effectively aged to her early/mid twenties, while Colossus has apparently stayed the same age as always. The two resume and then consummate their relationship. It's greeted with the reaction of "About time" from Wolverine.
The 1981 storyline Days of Future Past depicts a Bad Future in 2013, where Kitty appears as a middle-aged woman. X-Men comics eventually reached 2013, and Kitty is decidedly not middle-aged.
Variations of Kitty Pryde's lack of aging can be seen in the entire New Mutants generation of X-Men introduced in the 80s, who are maybe five years older than characters introduced nearly twenty years later.
Kitty managing to eventually reach her twenties is thanks mostly to Warren Ellis writing her into a relationship with the thirty-something Pete Wisdom; his hands were tied with Kitty to a certain extent, especially in how much leeway he had to show the, shall we say, nature of her and Wisdom's relationship. He's said in Q & A's that he personally thought of her being nineteen or twenty (which would've left her and Wisdom with a relatively harmless ten-year adulthood age gap), but that the Marvel bosses didn't want to age her too much. It was eventually addressed in, of all places, an ''Excalibur'' letters page, where the editors were of the opinion "Kitty's a mature girl in her late teens, and she and Wisdom are kind of like Han Solo and Princess Leia."
Kitty's age somewhat broke the X-Continuity back in the early '80s. She was introduced in 1980 at the age of 13 1/2, and was described as being "not yet 15" in a 1983 issue. So far this is normal. Except at the same time, Chris Claremont had tied his hands somewhat by explicitly pegging Jean Grey's death as occurring on September 1, 1980, and then doubling down by having characters refer to her death in terms that seem to imply a bit of real time progression (for instance, in another 1983 issue, Professor X talks of Jean's death as being "years ago", no doubt meaning three years ago). 13 1/2 to almost 15 is only 18 months at maximum, and probably lessnote meaning that the stories could only take place in very early 1982 at the latest. So either Kitty has a mutant power to stop aging, or Chris really should have left the actual date of Jean's passing vague.
Jubilee is in a worse boat then Kitty. She was about fifteen when she was introduced in 1989 and then spent the thirty years of real time that followed struggling to reach her late teens. By the time of the "Curse of the Mutants" arc, she had only been allowed to officially age two years (making her 17) despite having lived through a decent amount of MU history as a veteran member of the Claremont-era X-Men, and despite being a peer of the aforementioned Kitty, who can't be more then five years older then her and yet was a young adult at same time that Jubilee became a vampire in said arc without even leaving college age. The vampirism could've given her an out via no longer aging, but she was subsequently cured a few years later and now it's not really clear what age she's supposed to be. She seems to have been allowed to age up to adulthood, as she is now written pretty firmly as if she is in her early twenties, older then most of the 2000s era X-Men but slightly younger then people like Kitty or Spider-Man. How this works with her being a vampire for a couple years is anyone's guess.
Domino had to be at least 40 when she was first introduced. Then Progressively Prettier kicked in and she's actually aged backwards to the point where she's always drawn as a woman in her 30s. It's best to not think too hard on this and just accept it since Comic-Book Time is the only explanation there is.
This is also true of Emma Frost, maybe to an even greater extent considering she was introduced in 1979, where, for around 15 years, she was drawn to look like a very well-preserved MILF and usually written as of-an-age with male characters like Professor X, Sebastian Shaw and Banshee, all of whom were established to be at least well over 30, maybe even over 40. After her Heel–Face Turn, especially once she became a full X-Man herself, she was de-aged to look maybe 30 at the most. Part of this was to make her romance with Cyclops more palatable. In her mini-series she was expressly shown as being roughly the same age as the founding X-Men, and she described herself as being 28 in New X-Men. If this is true, she didn't just look mature in the early 80's, she also behaved like a woman who had lived a while and seen much, apparently at 20ish years.
One of the more visible examples is the death of Jean Grey during The Dark Phoenix Saga, where her tombstone gives her date of birth as 1956. This would have made her seven years old when she joined the X-Men in 1963.
In a bizarre inversion of this trend, Beast somehow went from a person who hadn't entered college yet (and might not even have been eighteen yet) in X-Men #66 (March 1970) to a person with a Ph.D. in Amazing Adventures #11 (March 1972). In other words, in only two years of real world time, enough time had somehow passed for him to go from being a high school grad to a doctor, somewhat like a comic-book case of Soap Opera Rapid Aging Syndrome. They even mentioned he was having his 30th birthday in a few days/weeks' time in an early '90s issue of "Adjectiveless" X-Men.
Another inversion happened with Professor Charles Xavier. In the very first X-Men story, he states that he is a mutant because his parents worked on the first atom bomb. This would mean that he was born in the 1940s; in other words, in 1963, he must have been in his very early 20s. Some time later, with the introduction of the Juggernaut, it is revealed that Charles and his step-brother had served in the Korean War together, which meant that in the mid-1960s, they should both have been around 30. And in the early 1980s, when Chris Claremont greatly elaborated on the origins of Magneto and Charles Xavier, it was revealed that Charles is apparently roughly the same age or only insignificantly younger than Holocaust survivor Magneto (putting both of them into the mid-to-late 50s at the time these stories were written) and that he had fathered a son with another Holocaust survivor, Gabrielle Haller. The son in question, Legion, is another example of this trope, as both of his parents having been alive during World War 2 should logically make him a bit older than he actually looks, yet he's still depicted as being nebulously somewhere in his early 20s (around the same age as the New Mutants).
Magneto and his family are also an example of this. When his backstory as a Holocaust survivor was first established in the 80s, nothing seemed off about it. However, as the years progressed, this has continued to retroactively age him. While Magneto's youthful appearance has been Handwaved as the result of an incident where he was restored to his physical prime by a Shi'ar agent, the effect the timeline drift should logically have on his children has never quite been addressed. It was originally established that he'd fathered Scarlet Witch and Quicksilver some time after World War 2 but before he'd actively turned to villainy, which would have put both twins in their late 20s or so in 1979, when this information was first revealed in The Avengers #186. However, as the years have worn on, the twins have aged maybe a few years at the most, as has Polaris, who was later retconned to be another of Magneto's children. While it's not unreasonable to buy that Magneto was already middle-aged or even elderly when his kids were conceived, that still doesn't change the fact that he met Magda, the twins' mother, even before he was sent to a concentration camp. Like the Legion example above, having two parents who were born in the 1930s (at the latest) should make Scarlet Witch and Quicksilver a good deal older than they actually are, but both heroes are still always depicted as being around the same age as the original founding X-Men. On his Formspring, former editor Tom Brevoort implied that this problem was part of the reason for the later Uncanny AvengersRetcon that established the Maximoffs were the twins' true biological family all along, thus removing the Magneto connection and the timeline problems it raised.
Likewise, several members of the team had origins tied to other events from history, such as Storm having been orphaned during the 1956 Suez Crisis and Sunfire getting his powers from the radiation his mother was exposed to at the atomic bombing of Hiroshima in 1945. This made sense when the characters were created in the 70s, but became less and less plausible with each passing decade. Notably, the 2007 Storm mini-series retconned things so that her parents were now killed in a generic terrorist attack rather than in a bombing from French forces. Sunfire, meanwhile, has simply never had his Hiroshima connection mentioned again; now his nuclear fire powers are simply his natural mutant ability, not related to anything involving his parents.
All-New X-Menlampshades the use of Comic-Book Time. The original X-Men still dress and act as though they came from the 60s, but Iceman is shown to be a fan of Run–D.M.C..
Young Cyclops is seen being baffled by stores selling bottled water, wondering what happened to our water supply, though we have had bottled water everywhere for decades now. Meanwhile in Champions (2016), when the other kids talk about how they used to watch Avatar: The Last Airbender when they were younger, Cyclops recalls that Seinfeld used to be his favorite show.
In the 80s, the members of the New Mutants were shown to be huge fans of the Magnum, P.I. TV show. During a later crossover between the X-Men and Shang-Chi in the 90s, a reference to Magnum P.I. had to specify that Cannonball had actually watched reruns of the show when it was airing in syndication, as it'd been cancelled nearly 9 years ago at that point.
The same writer behind All-New X-Men previously did something similar with Alias. The book was written in the early 2000's, but Jessica Jones was retroactively established as having been one of Peter Parker's high school classmates during the Silver Age. Whenever we see flashbacks to her high school years, people dress and act like they did in the old 60's Amazing Spider-Man issues, despite the actual time frame likely being the 90s.
In The Infinity Gauntlet (published in 1991), Doctor Doom states that Adam Warlock died "nearly a decade ago" during a battle with Thanos. The actual issue where Warlock died came out in 1977, a full 14 years earlier.
The Punisher: Frank Castle was initially a veteran of The Vietnam War, and his military background is often part of his stories, as it explains why he's such an effective vigilante. He was later retconned as veteran of the Iraq War, and in 2019 of the fictional Sin-Cong conflict. This, however, does not apply to the comics from The Punisher MAX universe, as Garth Ennis has full creative control of it and is free to narrate his own stories with the character, divorced from traditional continuity or tie-in to crossover events. In those comics, Castle was kept a Vietnam veteran, comic book time be damned (and his age is a factor in his death).
Another war veteran who has been updated is Spider-Man's classmate Flash Thompson. In the Marvel wiki entry for Gwen Stacy (who died in 1973) mentions Flash going to Vietnam. Flash's own page might have him in the category "Vietnam War characters", but the only war that appears in the text itself is the more recent Iraq one.
Another exception: Virtually all comic book universes created by Jim Shooter. All stories that took place in The New Universe, Valiant Universe, Defiant Universe and Broadway Universe unfold in real time, and the characters aged accordingly. (Unfortunately, only one of these got enough stories under its belt for this to have significant effects).
When the New Avengers did a guest spot, it was explicitly stated that Luke Cage fought Tombstone as Power Man three years earlier, and Spider-Man wore his black costume when Chase (who was nearing his eighteenth birthday) was in grade school. However, it plays it straight for its own timeline; the series has been running since 2003, and only Chase and Molly have had birthdays, but the references to years keep changing.
A issue of Runaways (Rainbow Rowell) confirms that two years have passed since Gert's death, which was eleven years ago in real time. But since the Runaways have been affected by major crossover events during that time, in theory that would mean that both Civil Wars, Secret Invasion, Secret Empire, Infinity, Inhumanity, AXIS and so on all happened in those two years.
So, which war/conflict was Iron Man injured in again to get his chest plate? Rule of thumb for that: Whatever the big international crisis-point was 8 to 15 years ago (so currently it is generally regarded as the Middle East or Afghanistan).
In Civil War II, James Rhodes refers to the War Machine armor as Tony's "late-eighties hand-me-down," though he could've been joking.
Captain America is a bizarre example. He is inextricably tied to World War II (attempts to extricate him to the 1950s Red Scare failed dismally), so he became a Human Popsicle in about 1945. He was unfrozen... about a decade ago, maybe? Steve was originally thawed in the 1960s, a mere 20 years after he was frozen, so not everyone he knew was dead (just middle-aged, while he was still barely 25) and he was around to experience things like The Vietnam War, The Civil Rights Movement, Watergate, and so forth. Writers have mined a lot of material out of having a Fish out of Temporal Water like Cap react to current events, but thanks to Comic-Book Time, the length of time he spends frozen keeps on growing, and the historical events he's witnessed or reacted to as they occurred have to keep being retconned. The most recent retelling of his origin, Captain America: Man Out of Time, has him coming back (presumably early) in Barack Obama's presidency. Keep in mind, one of his more memorable storylines, where he renounces the identity of "Captain America," involved him becoming disillusioned with someone who is heavily implied to be Richard Nixon. In modern continuity, Steve was frozen for seventy years, and missed all that, and the implied Nixon lost that implication.
The fallout from the aforementioned Nixon incident led to a followup story where Steve became so disillusioned with America that he abandoned the Captain America mantle and developed the new costumed identity of Nomad. The storyline in question began publication in 1974, and explicitly stated that Steve had been thawed out and found by the Avengers 10 years earlier in 1964. The hundreds of issues published in the years since then have likely compressed the timeline a bit so that Cap's Nomad phase now happened much sooner than a decade after his return.
Related to this, Sharon Carter was originally introduced as the little sister of Peggy Carter, a resistance fighter Cap had met and fallen in love with in Nazi-occupied France. Since Sharon was introduced during The '60s, the idea of her having a big sister who was old enough to have fought against the Nazis was entirely plausible. However, as time went on, Sharon's age went largely unchanged, which presented problems for Marvel, since like Cap, they wanted Peggy to remain tied to WW2. This ultimately resulted in Sharon being Retconned into being Peggy's great-niece, so that she could keep the familial relationship without having a sister who was decades older than her.
Both versions of Baron Zemo have also been subjected to this.
The first Zemo to appear, Baron Heinrich Zemo, was a Nazi scientist who'd battled Cap during World War 2, while his son Helmut had been a young child during the conflict. When Heinrich first appeared in The '60s as an enemy of the Avengers, it was established that he'd gone into hiding in South America after Hitler's defeat, with him having aged less than 20 years since the end of WW2. This was not much of a stretch at the time, nor was it when Helmut first appeared in 1973 as a man in his 30s, which lined up with the idea that he'd been born in the late 1930s or early 1940s. However, as time has gone on, this Nazi connection has retroactively aged both characters greatly, with Helmut in particular now being far too old to have looked like a spry young man when he first showed up. The later Thunderbolts: Distant Rumblings one-shot by Kurt Busiek attempted to rectify this by revealing that Compound X, the chemical Heinrich had developed during the war, possessed anti-aging properties that had allowed both men to remain young and strong despite so much time having passed.
Adaptations have had to come up with similar workarounds. The Avengers: Earth's Mightiest Heroes made both Zemos into a Composite Character who was kept unnaturally young by genetic treatments that "evolved" his body. Avengers Assemble, on the other hand, initially introduced Helmut Zemo as a scrawny old man with his World War 2 origin intact, but then had him gain his younger, stronger comic book appearance after using a Super Serum developed by his late father. The Marvel Cinematic Universe, meanwhile, completely removed the Nazi connection from Helmut's origin and has him around the same age as his actor, Daniel Brühl, who was in his late 30s when Captain America: Civil War was filmed.
The Invaders, a Marvel World War II-era superteam, were touched by Comic-Book Time in an unusual way.
Some of them, like Spitfire, aged in real time (only to be aged down again later), others were ageless (Human Torch was an android while Namor ages much more slowly than humans), others frozen (Captain America and Bucky), and a handful were just left to reach old age (Toro). However, look up how long Captain America was frozen for, and you'll find that the value has changed repeatedly, of course.
Toro was originally the Human Torch's Kid Sidekick. After the war, he retired before eventually returning in a 1969 issue of Sub-Mariner, where he was now an adult. He was killed off after this, and remained dead for decades, before being revived around the time of Dark Reign in the Avengers/Invaders maxi-series. Despite supposedly being revived at the same age he died (which should logically have happened less than a decade ago), he still looks to be in his late 20s or early 30s at the oldest. Strangely, his ex-wife Ann also looks too young to have been married to a WW2 veteran, despite not even having the handwave excuse of dying and being resurrected.
Doctor Yuriko Takiguchi, a Marvel Comics character that originally appeared in the Godzilla: King of the Monsters comic, is an interesting exception. When he originally appeared, he was already a middle-aged man. When he reappeared in the Uncanny X-Men, he aged quite visibly, which would make sense if one was to assume that in Marvel continuity, Godzilla comics took place in the same time as they were printed (mid 1970s). The thing is, though, Godzilla comics took place in the then-contemporary Marvel Universe, and many characters that age in Comic-Book Time appeared in supporting roles.
Subverted with the Young Avengers; while the original artist Jim Cheung always drew the team as teenagers, the kids actually aged as the series continued. They started as 15-16 years old; by the time of Avengers: The Children's Crusade, they are between 16-17 and new writer Kieron Gillen acknowledged in his Formspring that the ages of the members on the new team (bar Kid Loki) are between 17-19, putting the original members in the 17-18 age (since Kate Bishop, Noh-Varr and America Chavez are acknowledged as the older ones in the team, the first two being stated as 21).
Kieron Gillen has mentioned that the passage of time is actually relevant. He compared the original series to high school, and the relaunch to post-graduation.
Clearly, though, Gillen and Hawkeye writer Matt Fraction didn't do as much discussion of Kate's age as Gillen claimed, as Kate is said to be "a teenager" and "old enough to be your [some businessmen's] daughter's younger, cooler, and a little more worldly best friend", both of which are from issues that came out almost a year after Kate was stated to be turning 21, so she seems to be stuck in comic book time a little.
That said, the characters themselves are a massive Continuity Snarl when it comes to their ages. If Teddy was conceived during Captain Marvel's brief time together with Princess Anelle during The Kree/Skrull War storyline, then he could have been born no later than 1973 unless Skrulls have a much longer gestation period. Regardless, Anelle was killed when Galactus devoured the Skrull throneworld in 1983. Then, if Comic-Book Time is applied to the Kree/Skrull War, there's no way the conflict took place long enough ago for the currently 20-something-year-old Teddy to have been conceived during it. Meanwhile, his boyfriend Billy was born for the first time in 1986, and "died" in 1989. Allowing for some time spent dead and then experiencing Reincarnation, being born into a new biological family and growing into his teens so as to match Teddy's age when Young Avengers launched requires that Soap Opera Rapid Aging Syndrome be added to the mix for both Billy and his twin Tommy. The 2020 Empyre: Emperor Hulkling one-shot implied that time travel may be responsible for Teddy's inexplicable age, with Anelle claiming she sent him "through space, through time" as a baby.
Billy is later seen attending a drag brunch and ordering alcoholic drinks in a War of the Realms tie-in, implying that, like Kate, he's now at least 21.
Interestingly, Eli Bradley and his mother, Sarah Gail. In the first issues of the original run, Eli is mentioned as being a part of the fail-safe program created by The Vision, with his being a super-soldier (or so everyone thought) being noted. Cap points out that Eli couldn't have received his super-soldier powers through Sarah Gail, since she was born prior to her father Isaiah receiving the serum. Isaiah received the serum in the 40's, before Cap, putting Sarah Gail at around 45-50 in the late 80's when Eli presumably was born (if he's a teen in 2005). On top of that, Sarah has several other children besides Eli. Being in her 40's when she had Eli isn't out of the realm of possibility, but it's certainly rare.
As noted here, Stature is a weird inversion of this, basically suffering from the comic book version of Soap Opera Rapid Aging Syndrome. Cassie Lang was explicitly stated to be 14 years old when she first joined the team (even though she usually looks much olderDepending on the Artist), but in her last few chronological appearances before the series started, she looked significantly younger. She somehow aged several years in the year or two (real world time) between Geoff Johns' Avengers run and the start of Young Avengers, with no explanation given.
The Power Pack are a particularly bizarre example. They started out as a group of kid heroes, all aged 8-11. Two of them remained kids, while Alex Power appeared to be about 18 in Fantastic Four, and Julie Power seemed like she was in her mid-twenties when she showed up in Runaways and as a member of The Loners. As a crowning absurdity, the Power Pack got a series of mini-series with the kids promptly brought back to their original ages.
These minis were later declared non-canon, and when Julie eventually joined the Avengers Academy, she once again looked to be in her late teens.
Meanwhile, her older brother Alex has become a member of the Future Foundation, but now appears to be about five years younger than her.
Power Pack also further complicates Franklin Richards. As a sometime member of that team (as Tattletale), he wasn't too much younger than the kids. Now compare his age today with that of Julie and Alex.
Civil War II somewhat confuses the timeline, Julie is de-aged yet again in an anthological tie-in, and the tie-in Spider-Man 2099 arc seems to justify it with them appearing in 2099 where they offhandedly mention their powers make them Long-Lived. Except they turned out to be Skrulls who forgot their true identities so who knows how accurate that inference is.
A short-term example happened for Daredevil during the Inferno (1988)Crisis Crossover: He gets beat up by an assembled gang of his enemies and dropped in a ditch during a Fourth of July parade. He gets out of that ditch and vaguely healthy again just in time for the Christmas issue, implicitly no more than a week or two later.
Daredevil has run into this with the 2015 Netflix series. Critics have noted that the crime and gang-infested Hell's Kitchen presented in Daredevil made sense at the time that the storylines being adapted were written (in the 1960s-1980s), but nowadays Hell's Kitchen has long since gentrified and New York in general has far less crime. The show's explanation for this is that Hell's Kitchen took massive damage during the Chitauri invasion.
Justifiably averted for Doctor Strange, who met Death as part of his trials to become Sorcerer Supreme: the encounter locked him in the age he was when it happened (his mid-forties), where he has remained ever since. According to the Marvel: The Lost Generation miniseries, Doctor Strange's origin really did happen in the Sixties, and perhaps even earlier.
In Christopher Priest's Black Panther run, it was shown that Captain America fought alongside T'Chaka, T'Challa's father, during World War II. As the years went on, the initial meeting had to be Retconned so that the past Black Panther Cap had teamed up with was actually Azzuri the Wise, T'Challa's grandfather.
Black Widow was retconned into possessing slowed-aging because of this trope. It was getting increasingly harder to believe a youthful woman like her was a veteran of the Cold War, so the writers decided to get around this by effectively giving her eternal (or at least longer-lasting) youth.
Ah, the infamous 9/11 Very Special Episode of Spider-Man. The writers wanted it to be an out-of-continuity stand-alone issue, but Marvel's editors insisted on it being part of an ongoing book. Amazing Spider-Man #36 (from late 2001/early 2002 — not the one from the 60s) got the honors. Ignoring the myriad Fridge Logic issues of 9/11 even happening in the Marvel Universe, tying this issue to a definitive, specific moment in history means this almost certainly isn't in continuity anymore. As of now, Spider-Man was in high school (and maybe hadn't even received his powers yet) in 2001. That famous picture of Captain America saluting in front of the smoking ruins of the towers? Cap didn't get thawed out until the Obama administration. One understands the noble reasons why this issue was written, but trying to wedge it into the already confused timeline of Marvel Comics makes it stick out like a sore thumb.
Legion of Monsters vol. 2 shows Morbius in a flashback that takes place in in-universe 1973, and says he had been a living vampire for years at that point. This would mean he must have aged 40 years by the time the comic came out in 2011 but that does not work at all with the rest of the Marvel timeline: other characters Morbius had run into before the flashback storyline took place would also have had to have aged at least 40 years, but haven't. For example, Peter Parker became Spider-Man in a comic released 9 years prior to the one in which Morbius becomes a living vampire, but in a 2014 comic states he has been Spider-Man for 13 years (so some simple calculations reveal Morbius could only have been a living vampire for about 10). The flashback also shows Morbius wearing some very groovy 1970s clothes, which ironically he never wore in comics actually released in the 1970s.
The central concept of Marvel 100th Anniversary Special, a series of one-shots published in 2014, supposedly from 2061. While normally 20 Minutes into the Future comics feature successors to the current heroes, these ones take the view that in the comics Marvel actually publish a half-century from now, most characters will be basically the same age they are now.
The 75th anniversary magazine Marvel put out contained a short story showing the first flight of the Fantastic Four, which marked the beginning of the Marvel Universe. A young Kamala Khan is shown playing with her toys as the rocket launches, providing a very poignant connection between the start of the Marvel Universe and its present day status. However, some pointed out that if taken literally, the story would seem to imply that the entire history of the Marvel Universe from the Silver Age to the present has occurred within 10-13 years or so.
Similarly, Mark Waid's 2017 run on Captain America starts with a flashback to one of Steve's first adventures after being unfrozen, back when most civilians didn't even recognize him in-costume. We then jump to the present day, ten years later.
This was used as a weapon of sorts in Spider-Verse. Big Bad Morlun waltzes into the Spider-Man Newspaper Strips universe, ready to snack on the Peter Parker of that universe. However, as Peter and Mary Jane act strangely, Peter repeating himself over and over, Morlun's left utterly flummoxed at this before realizing what's going on, that time flows differently in this universe and that it might be weeks, even months before he can actually eat Peter! The Master Weaver uses it to spirit Morlun away and hide the universe in a pocket dimension, claiming that the world was temporally unstable. Morlun buys it without a second thought, just too disturbed by the changes.
Sort of used in Marvel's Transformers Generation 1 comics. The Transformers on the Ark awakened in 1984, and that date remained consistent for the entire run; thus, in issues printed in 1989, a couple of characters mention having been active for five years. Also, Simon Furman's future stories always take place exactly 20 years after the mainline stories; thus, the future segments of "Target: 2006" take place in 2006, while those of "Time Wars" take place in 2008. However, Buster and Jessie never seem to advance through high school, nor does Spike graduate from college. (Granted, these are very minor quibbles, but it's still noticeable).
Joss Whedon's run on Astonishing X-Men got badly out of sync with the rest of the Marvel Universe due to its heavy Decompression and Schedule Slip. For how bad things got, during the second arc, Charles Xavier and Magneto are hanging out on the wrecked island of Genosha (so prior to the House of M event), but by the final issue Spider-Man is making jokes about Civil War having happened. The events within the comic happen over a couple of weeks at most.
Lampshaded in the Worst X-Man Ever mini-series, which takes place on an alternate but still quite similar version of the Marvel Universe. The final issue reveals that Miranda has been using her Reality Warper abilities to "revise" the Marvel Universe for decades, making sure that the heroes never grow old or die for real. She states that (among other things) she's the reason Tony Stark has been in his 30's since 1963, as well as the reason why the X-Men have been constantly reinvented since the Silver Age.
In The Ultimates (2015)Galactus of all people explains the trope itself (the now is always now but its "gravity" pulls some past events behind it, while others (actual real world history) remain fixed), when the team tried to avert a suspected Time Crash by assessing the damage done to the timestream by the rampant misuse of Time Travel. Turns out the flexibility given by comicbook time makes the timestream very resistant to paradoxes; you may destroy yourself with them but time itself will arrange itself back eventually. After the lecture, he admits it's a very simplified version of events. Unfortunately, this has lasting side-effects, leaving Carol Danvers - who was on the receiving end of the vision - a little bit unglued, partly leading to the tragic events of Civil War II as she tried to re-establish some control.
An issue of All-New, All-Different Avengers features a flashback to the original team planning an attack on Doctor Doom. Everyone's wearing their classic costumes, but we also get this exchange:
Captain America: Rick Jones's shortwave — Iron Man:Social media. Cap:Whatever...
In an issue of Uncanny X-Men, the X-Men have just watched The Empire Strikes Back in theaters. This could be HandWaved as a re-released showing, but they discuss the movie as if it has just come out.
Deadpool has had enormous fun with this trope, milking it for everything it's worth and then some. He's time traveled back to the time in the 1960's when Spider-Man fought Kraven, and had fun lampooning the ridiculous 60's fashion, slang, Comics-Code enforced family friendly minimal violence, the fact that the current Spider-Man would not have even been born, that Kraven's name actually means cowardly/weak, etc. He also traveled back in time to meet the 1960's-era Fantastic Four and was just as manic and incomprehensible with them.
Deadpool: (Peering around the panel he's in, looking at the artwork and lettering) Let's see...Kirby/Sinnott...this is 1967, right?
Reed Richards: I have no idea what you're talking about.
In another comic, he's revealed to have existed back in the seventies, wearing a ridiculous afro and "teaming up" with the Heroes for Hire, while also having fathered a daughter - who back in the present day (the comic was published in 2013) was still a child.
The 2016 Power Man and Iron Fist series opens with the duo reuniting with their old assistant Jennie, who has just finished serving a five year prison sentence. The incident that landed her in prison occurred in the 2011 Power Man and Iron Fist mini-series, which was indeed published roughly five years prior in real world time. Oddly, Luke Cage's daughter Danielle had already been born by the time the 2011 book happened, even though she is still depicted as being younger than 5 or 6 years old in the 2016 volume.
In the Comixology-exclusive Avengers: Back to Basics mini-series from 2018, Kamala Khan is sent back in time and inadvertently becomes a founding member of the Avengers. When her mother is accidentally killed in this time period, Ms. Marvel figures that she only has a few years to live before she catches up to the day she was born, thus erasing her from existence. For reasons pertaining to this trope, we get no specific dates, but it still carries with it the implication that 50+ years of changes both within the Marvel Universe (everyone’s costumes have since been redesigned, they all talk in that era’s speech patterns, etc.) and broader cultural trends (like the Avengers not understanding when Kamala identifies herself as “Ms.” instead of “Miss” Marvel), all happened in less than twenty years.
One of the most infamous moments of the original Civil War event was a tie-in where journalist Sally Floyd accused Captain America of being out of touch with modern Americans because he didn't use Myspace. Even at the time, critics claimed that was a reference that would become dated extremely quickly, so a later Secret Empire tie-in Retconned the interview slightly to change the website she'd grilled Cap about into Twitter.
Generations revolves around a mysterious and timeless realm called the Vanishing Point, where modern Legacy Characters like Miles Morales, Amadeus Cho, Laura Kinney, Kate Bishop and Kamala Khan encounter their predecessors at various points in Marvel history. Nearly all of the stories are seemingly set in the past (except for the Ironheart / Iron Man team-up, which takes place in the future), and some of them ape the visual aesthetics of the era those original comics were actually published in (The '60s for Spider-Man, The '70s for Ms. Marvel, and so on). However, with the exception of the team-up between Sam Wilson and Steve Rogers (which sees Sam sent back in time to World War 2), the actual time periods are kept vague, with no explicit years ever given. Despite this, there are clues given to indicate just how far back these events are seemingly occurring, such as the Ms. Marvel issue treating the Women's Lib movement as a relatively recent development, or Logan seemingly not knowing what a cellphone is in the Wolverine installment.
In the 2019 limited series Avengers: No Road Home, Monica Rambeau claims to have gotten her powers (which occurred in a story published in the early 1980s) less than a decade ago.
History Of The Marvel Universe: The miniseries fixes the issue of Comic-Book Time regarding war veteran characters by creating the Siancong Conflict, a war with the fictional Asian nation of Siancong, which first appeared in Avengers #18 (July 1965) as "Sin-Cong". The miniseries establishes that characters that were originally written as having fought in Vietnam (The Punisher, War Machine, Arclight, etc.) as well as certain characters previously stated to have fought in WWII (Mister Fantastic, The Thing) had actually fought in the Siancong Conflict, making it more convenient to accommodate for the timescale.
This explicitly includes the comic actually called The 'Nam, which was supposed to be a realistic portrayal of the conflict, but did feature Frank for Wolverine Publicity.
In Jane Foster: Valkyrie, a specific age was given for Jane. It turns out that despite appearing in early Thor comics, then marrying, having a kid and becoming a doctor after her years of being a nurse, Jane is a millennial and only 33 years old.
Marc Spector has long moved past the point where his earliest adventures as Moon Knight could take place in the 1970s, when they were published. Danny Lore took advantage of this to introduce a '70s Fist of Khonshu in Moon Knight (2021) #20's backup story who once teamed up with Blade.
(who died in 1973) mentions Flash going to Vietnam. Flash's own page