Ace Combat gives us Old Aces. In a line of work where pilots usually retire or get promoted away from a cockpit around their mid-to-late-thirties, we have:
Ashley Bernitz, aka 8492th squadron leader / Grabacr 1 in Ace Combat 5: The Unsung War, a 30-years veteran who is still a top-notch pilot and leading member of The Conspiracy. He is 53.
In the same game, Pops the resident mechanic turns out to be legendary Belkan ace Wolfgang "Huckebein the Raven" Buchner, Bernitz's personal Nemesis. And he still got it, as he manages to escape an enemy squadron in end-game planes using only his skill and a trainer jet. He is in his late fifties.
Mihaly in Ace Combat 7: Skies Unknown is old enough to have grey hair and two teenage granddaughters and needs special equipment to operate his plane, putting him in his late fifties to mid sixties. He still shoots down anything not controlled by a player like it's nothing.
Akatsuki Blitzkampf has the local Mighty Glacier, Fritz, a quiet swordsman in his 70's or 80's who is incredibly badass and is one of the very few cast members who's a survivor of the past war from fifty years ago.
In Assassins Creed, the single most dangerous opponent you can face in a straight sword fight? Your own ancient, gray-bearded master, Al-Mualim, in the final battle. He uses extensive trickery. Being able to magically multiply yourself has some clear advantages in battle.
Although his true age is unknown, La Volpe from the sequel is clearly no spring chicken as his wrinkled face shows. Nevertheless, the first time Ezio meets him, the former is winded trying to keep him.
Augus from Asura's Wrath, a Cool Old Guy who is quite fond of the finer things in life and has quite the Blood Knight streak to him. Unfortunately, he's also one of the Seven Deities who Asura has sworn vengeance against for betraying him. The battle you have against him is one of the most awesome ones of the game.
Fo Fai from Battle Arena Toshinden. According to the manual, he's 103 when the first tournament starts.
Hermit Cat is an elderly cat who resides on floor 30 of the Heavenly Tower, but is still a powerful martial artist, and loves showing up rich kids who think they can just buy enlightenment. Master Uril on the top floor also qualifies, given how he's the retired head of a powerful clan who still rules in secret, sealed away the Demon King long ago, and can use powerful surge attacks.
The enemies from the September event, Old Guys About Town, are elderly versions of the standard enemies who've mastered martial arts. Kung Fu Cat X, the drop from the event, is equally old and equally adept with his fighting style.
The magician Patrus from Betrayal at Krondor is a hardy old geezer. It doesn't matter if you're a tough dark elf fighter, mess with him and you'll be disposed off in an unceremonious huff.
For that matter, Gorath also qualifies, after surviving in a position of leadership in a cutthroat society for close to two and a half centuries.
There's also Eileen the Crow, the Hunter of Hunters, a very old woman who's tasked with hunting down Hunters who've gone mad or become infected with the scourge of beasts. In her case though, the trope is deconstructed: Her stubborn refusal to accept that she's passed her prime and is in no shape to hunt down her marks any longer ends up with her own death if you do not come to her rescue.
Sensei in Club Penguin is the oldest penguin in the game, and a master of Card Jitsu. He trains penguins to become ninjas, and has to be challenged (and defeated) in order to become a ninja.
In the series backstory, Frandar Hunding was the legendary Yokudan/Redguard Ansei, or "Sword Saint", who is quite possibly the greatest Master Swordsman in the history of Nirn. After winning 90 duels against rival swordsmen, Frandar retired at age 30 and retreated to Mount Hattu, where he wrote his legendary treatise on swordsmanship, the Book of Circles. At age 60, a group of Ansei, led by his son Divad, came to him and asked him to lead them in battle against the Yokudan Emperor Hira, who was attempting to consolidate power by eliminating the Ansei. Frandar reluctantly led them to victory, but at great cost. Due to being considered "red with blood" by the citizens of Yokuda, he chose to self-exile to Tamriel, becoming one of the first Yokudans to settle there. Later, pushing 90, he was still acting as a Frontline General when he finally fell in battle against the giant goblins of Hammerfell.
Also from the backstory, Chimeri Lord Nerevar was (at least) in his 300s at the time of his death and was still serving as a Frontline General, having infiltrated the Dwemer Red Mountain stronghold. Granted, the races of Mer are Long-Lived compared to the races of Men, but not counting those who've enhanced their lifespans with magic or divine powers, that is still quite old for a Mer.
In Morrowind, BladesSpymaster and initial main quest Quest Giver Caius Cosades is a balding, gray-haired old man. However, his stats and skills are better than most. He even fits the martial arts basis of the trope, being one of the highest level trainers of the Hand to Hand skill.
The series has the Greybeards, masters of the Thu'um (the draconicLanguage of Magic). The Greybeards have trained their voices to such an incredible extent that even a misplaced whisper could kill a person. They play a major part in Skyrim, where they summon the Dragonborn to High Hrothgar, their monastery on the Throat of the World, the tallest mountain in Tamriel, for training in the Thu'um. When they greet the Dragonborn with a politely whispered "Dovahkiin", the whole mountain shakes from the force of it. When they speak in full voice to summon the Dragonborn to High Hrothgar, all of Skyrim hears it. It should be noted that this isn't just lore fluff, the four Greybeards are some of the highest level-NPCs in the game, with Arngeir sitting pretty at level 150.
EXTRAPOWER: Attack of Darkforce: Old man Roshi is an old karate master, now living in hermitage. His guardianship over Kojiro is why he's an excellent, if arrogant, martial artist today, and his skills haven't dulled with age. Unfortunately, he gets done in when an enhanced Half-Human Hybrid is brought into the equation.
Tung Fu-Rue and Jubei Yamada from the Fatal Fury series, along with Lee Pai-Long from Art of Fighting. Tung even made it as a bonus character in the PS2 version of KOF XI. Makes you wonder why they didn't form a team in KOF.
Tung continues his role as mentor in KOF, forming the new hero team in XIV with his final two disciples, Shun'ei and Meitenkun.
Final Fantasy XI has Maat, the old man responsible for raising the level cap from 50 to 75 (or just to 70 on a few expansion jobs). He uses both Wax On, Wax Off and Training from Hell methods to raise your limits, but you never take him too seriously, and think he's just an advisor... then you go to break the 70-75 cap, which has you fight him, and most likely see him gleefully rend you into paste, even unfairly so. Simply put, anyone who's 75 respects him. Or hates him. It kinda varies. Love him or hate him, you have to respect him. Even if you fought Maat as a Red Mage back in the days before he was nerfed, you have to smile when you see Maat whalloping the crap out of enemies in the past in the Wings of the Goddess expansion.
Final Fantasy XIV's Shadowbringers has Ran'jit who's this, as well as one of the main villains that consistently gets in the way of the Warrior of Darkness's path by being just about an Implacable Man.
Also from XIV is Hamon Holyfist, the leader of the Pugilists' Guild in Ul'dah. While advanced in age and given to lechery, he is guildmaster for a very good reason.
Master Li in Jade Empire, the question is, what's a man like him doing teaching a bunch of peasant kids out on the edge of the Empire?
Saisyu Kusanagi, Chin Gensai, Takuma Sakazaki, and a number of others from The King of Fighters. Three of them even team up in 98 to form the Masters Team: Saisyu, Takuma and Colonel Badass Heidern (despite them not being that old, compared to Chin). In KOF 2002 Unlimited Match, Chin joins the team in Saisyu's place, due to the game being a dream match for the 99 to 2002 editions and Bao occupying his position in the Psycho Soldier team. Lampshaded with their theme song, In Spite of One's Age, a soft and relaxing tune. You may want to hear the '98 version, and 2002 Unlimited Match version.
Master Xehanort in Kingdom Hearts: Birth by Sleep is the Big Bad of the game, and the entire first saga of the franchise, and is a hunched-over old man.note How old? His younger self is known in Japanese as Seinen Xehanort — "seinen" meaning 'young man'. The age of majority in Japan is 20 years. Kingdom Hearts III takes place 75 years after a cutscene late in Young Xehanort's career. That puts Xehanort at upwards of 84 in Birth by Sleep and north of 95 in III. However, in spite of his age he's still one of the most powerful entities in the series so far — in the cutscene before the final battles of the three storylines, he raises plateaus of earth into the air and creates a whirlwind of Keyblades to attack the heroes with, all with a few waves of the hand. And when one of the heroes, Ven, gets close enough to attack, Xehanort evades the sneak attack, holds Ven in the air by the head, and freezes him solid. Then the time the actual boss battle comes around, and he averts Cutscene Power to the Max by doing all of those things as attacks. However, he's not content with being unable to unleash his full power just because his body's too old and feeble to handle it, which is why he spends most of the game corrupting one of the heroes, Terra, so that he can steal his body at the right opportunity. As seen with the resulting Terra-Xehanort, as well as his younger self, he's even more horrifyingly powerful when he has a body that won't give out at a moment's notice.
Jolee Bindo in Knights of the Old Republic, who is old enough to be starting to lose his memory and for the little hair he has left to be completely white, and yet with the proper build and gear is a contender for the title of most powerful character (including the player) in the game at high levels. On the other hand he dismisses the idea of being a teacher and claims just to be travelling with you for fun.
The Legend of Spyro: While the four Dragon Guardians' age isn't mentioned, their words imply they're getting too old for the job, but that doesn't mean the Apes attacking the temple in the second game didn't get their butts kicked by the four of them. Yeah, Spyro and Cynder outclass them in the end, but that's what they were hoping for.
The Legend of Zelda: Breath of the Wild: The secret Final Boss of the DLC, Maz Koshia, is one of the wizened Sheikah monks you usually encounter at the end of a shrine, making him thousands of years old. Despite his supernaturally advanced age, he is a more capable user of Sheikah martial arts techniques than even Master Kohga, the leader of the Yiga Clan.
Sotaro Komaki embodies this trope in the games, being one of the fighting instructors from Yakuza 0 forwards, and being capable of teaching Kiryu everything from how to fight gun-wielding opponents to the immensely powerful Komaki Tiger Drop. He is also perfectly capable of kicking his pupil's ass, should the need arise.
Yakuza 2 adds Granny White, an elderly woman who trained (and kicked the asses of) Lau Ka Long and the Snake Flower Triad.
Replace "martial artist" with "cabaret club hostess", and this trope applies very well to Yuki, in her appearance in Kiwami 2. Yuki is at this point 39 years old, which is ancient for a hostess. However, what she lacks in youthful beauty, she more than makes up for in grace, poise, charm and skill. In spite of being nearly twice the age of her employees, she can still run circles around them without even trying when she works the floor. More impressively, she's still able to be a hostess in Infinite Wealth... At the age of 57.
By the later games, Kiryu, Majima and Saejima could be considered this since as of Infinite Wealth they're all pushing 60 but are still shocking dangerous for their ages. However, by that game age and cancer has sapped Kiryu's strength considerably in order to justify him fighting alongside Ichiban though he can temporarily tap into his old strength in order to ignore the turn-based combat and beat up enemies in real time.
In Live A Live, the player character of one chapter is a nameless old master of a dying school of Kung Fu in search of a young disciple to pass his art on to.
Magical Starsign: Master Macadameus is an old sage found on Puffoon, and according to his description, he's practiced every battle in his head a hundred times before the first blow has landed. He's a cool guy, giving the party battle tips, helping them free the monsters trapped within figurines, and letting them use bean pops on him to gain EXP... but attack him, and you'll regret it unless you're strong enough to beat the Bonus Dungeon.
Mass Effect: Beware of any krogan who has lived past the age of 1,000. Since krogan are predisposed to spend their lives in combat, very few of them reach old age... and those that do have probably seen more battles than every human in an army put together. Such krogan are often known as "Battlemasters" and are considered some of the most dangerous warriors in all of existence. Asari matriarchs (from a race that lives just as long as krogan) with combat training tend to also qualify, although they're less likely to be front-line specialists.
In the Mortal Kombat series, Bo Rai Cho fills this role. An ancient martial artist native to the Outworld who invented Drunken Fist, his many students include Li Mei, Kung Lao, and Liu Kang, the hero of the series. In the Konquest Mode of Mortal Kombat: Deadly Alliance, it states that he was also the sensei of the 17th Century samurai Musō Gonnosuke Katsuyoshi, who was a Real Life personality. And he's no slouch himself. In Deadly Alliance, it is stated that the only reason he never took part in the original tournament in an attempt to defeat Shang Tsung himself is because, as an Outworld native, Shao Kahn would get credit for his victory, which was what Kahn wanted in the first place.
In Ōkami, the sensei which teaches you new moves starts out when he first talks to you as a kind old man....but when you purchase a new move his head literally spins completely around, turning his giant chin into a giant forehead, and his long mustache into badass eyebrows, and his back straightens out, and his cane becomes a bamboo riding crop.
Played straight in Phantasy Star Universe with Headmaster Nav - the only difference being that he's a CAST (an android) who only looks like an old man. He's still almost 200 years old, though.
In Pokémon Red and Blue, there was originally going to be a battle with Prof. Oak, who apparently keeps the Pokémon neither you nor your rival chooses. He would have been the strongest Trainer in the game - even better than the Champion - but, for some reason, the battle was dummied out. However, using a GameShark, the battle can still be accessed.
Pokémon Sword and Shield has gym leader Opal who at 88 years old is definitely the oldest gym leader in her region and possibly the oldest trainer in the entire series. Looking at two of the League Cards will imply she was even Champion for a while until losing the title to another trainer who grew up to be this — Mustard of the Isle of Armor.
Ford Cruller, from Psychonauts, is a skilled and powerful Psychonaut who suffered brain damage in a fierce psychic battle a while ago. Now, unless he's near a source of Psitanium (like that beneath Whispering Rocks camp), he slips into a number of alternate personalities. So he works as Mission Control when he's not doing odd jobs around Whispering Rocks. He also ends up becoming Raz's psychic tutor.
The Owl, Wolf's adoptive father. The only man in the game to have the title "Great Shinobi". And he'll prove more than worthy of it in his boss fights, as even without his bag of tricks (ranging from shuriken and poison to firecrackers and smoke bombs), he's an agile old bird who can easily swing his massive sword around. This goes double for the slightly younger version of him in the second Hirata Estate memory, who's not only physically stronger than present-day Owl, but can summon an owl spirit familiar to aid him in battle.
Lady Butterfly is an elderly kunoichi who was one of Wolf's former mentors, and age hasn't stopped her from being a highly acrobatic fighter with incredibly powerful illusion magic.
Isshin Ashina, the patriarch of the Ashina clan, was known as the "Sword Saint" in his youth. While his age has long since caught up with him, his swordsmanship is arguably even more refined than during his prime; despite being terminally ill, he's still capable of easily slaughtering entire ninja squadrons in his guise as the "Tengu of Ashina", an alter-ego he also uses to secretly mentor Wolf in swordsmanship. In fact, the old man is powerful enough to be the final boss in one possible ending (in the other endings, he is revived at the peak of his power by his grandson Genichiro's sacrifice, and this version of Isshin is by far the most difficult boss in the game).
Sengoku Basara casts Yoshihiro Shimazu as one of these, a Master Swordsman who carries a BFS that would put the Buster Sword to shame and yet uses it with enough finesse to precisely deal One Hit Kills to any opponent. Many of the characters in the game revere him for his skills and seek lessons from him, for good reason.
Honard in Silver Falls Gaiden: Deathly Delusion Destroyers and Ruby River is a local archery expert and pioneered some techniques and equipment. He's also in his 90s, but maintains himself via daily training. He also has a 3D target course, which is popular with tourists. While he doesn't chage for lessons, he's always happy to teach anyone who's genuinely interested in archery.
Edge Master from the Soul Series. He is Kilik's master and can also use every weapon in the game with equal proficiency to its owner. One of the oldest, non-immortal characters in the series (though his actual age is unknown).
Gen. He's actually a Blood Knight in at least his '70s who is deathly ill, but prefers to die in a fight than succumb to his illness.
Gouken, the elder brother of Akuma and the legendary master of Ryu and Ken. Initially only known through backstory and rumors, he was finally made playable in the home ports of Street Fighter IV.
Oro from III, an elderly hermit who is 140-years-young and still more powerful than the average young fighter in their prime. So much that he voluntarily disables one of his arms just to even the odds for his opponent.
Paper Mario: The Master. While he appears to be asthmatic and weak, when he goes quite literally Super Saiyan on Mario, he turns out to be quite possibly the game's hardest foe.
Mario Party 7: The Star Space on Pagoda Peak is overseen by a wise old Koopa kung fu master.
In Super Punch-Out on the SNES, you fight a Chinese martial arts master called Hoy Quarlow. He is both the most unorthodox and most irritating opponent in the game, not so much for his difficulty (he is indeed a tough opponent), but for the fact he unabashedly cheats; half the time he doesn't punch you, but kicks you and hits you with his walking stick. In a boxing game. You can guess that he's That One Boss...
Master Rishu from Super Robot WarsOriginal Generation deserves a mention here. While being a side character who is only mentioned to be Sanger's teacher in the first game, and using a cane to walk, he was more than capable to take on multiple bioroids armed with automatic weapons while using only a sword, hidden in his cane. Later, in OG 2.5 he becomes an actual playable character, piloting Grungust type 0.
Wang Jinrei from the Tekken series. When he participates in The King of Iron Fist Tournament 5, he's 105 years old, has a bad back, and is somewhat senile. He can still send the young'uns tumbling across the arena with ease, however. Later, in Tekken 7, we're introduced to another old master in the form of Wing Chun practicioner Leroy Smith. He's at least over 50 years old and blind in one eye after getting shot, but he's skilled enough as a martial artist to have singlehandedly torn through several criminal gangs, as well as square off against people several years younger than him in and come out on top.
Thief: Artemus was Garrett's former teacher and the only person able to outsneak the Master Thief.
Master Zen, the ancient martial arts master in Tony Hawk's American Wasteland. For some reason, his teaching translate very well to skateboarding while still conveying supernatural abilities. He's also a total goofball, in spite of his wisdom.
and 2002 Unlimited Match version.