From The Legend of Zelda: The Wind Waker, we have Orca, who is an aged and avid swordsman. He practices constantly, and is Link's primary trainer in the ways of the blade. His intellectual older brother Sturgeon is exasperated by Orca's apparent refusal to exercise his brain in favor of sword practice, but surprisingly he himself used to be a talented swordsman in his younger days.
Ganondorf in The Wind Waker and Twilight Princess. The guy's always sealed up for generations, putting his age somewhere around the hundreds, if not thousands, and he looks the part too. And since he's the Big Bad, he's obviously going to be dishing out plenty of ass-kicking.
The entire 501st legion, of Star Wars: Battlefront. They were active from Geonosis until Hoth at least, and never accepted new recruits (they have always been composed of original Kaminoan clones), which counting growth acceleration and elapsed time makes them at minimum 45 years old and more probably around 70 years old biologically at the time of the original trilogy.
In The Legend of Dragoon, the only character in your entire party with the balls to fight dragons barehanded is Haschel, who taught the hero, Dart, martial arts a few years before the game began and is actually Dart's grandfather, although he doesn't find this out until near the end of the game.
Adam, from the Trauma Center series. He may not be able to move, but not only is he 121 years old, he uses his own body to manufacture deadly pathogens that border on the self-aware, plus his skin is dark grey with blue lines.
Sergeant Avery J. Johnson is a Spartan-I who served in classified Spec-Ops before rejoining the regular Marine Corps, and fought at both the first and last battles of the 28-year-long Human-Covenant war. He kills enough Flood to astonish the Master Chief himself, and successfully hijacks a Scarab. He even badmouths the Prophet of Truth to his face while being held captive and beaten by a Brute. He's probably at least in his 70s when you fight alongside him in the games; even taking into account cryo-sleep, he's still at least in his 60s.
While not a ground pounder, Captain Keyes certainly qualifies as well, being perhaps the UNSC's best single-ship commander, and is still quite capable of undertaking ground-ops if he has to.
Trema, the Bonus Boss of Final Fantasy X-2, fits this perfectly, being a little wizened old man who can kick your ass faster than you can blink, as well as being a complete aversion of the normal tendency for Bonus Bosses to be giant robots, cosmic horrors, or otherwise huge and improbable monstrosities.
Gen from the Street Fighter series. A professional assassin in his heyday, he's still capable of matching Akuma in his old age. Oro from Street Fighter III is over a hundred and is more or less the most powerful character in the series outside of Gill and Akuma. In fact, Akuma himself is old enough to be an example.
Actually, Akuma himself faces Oro, a match that apparently ends in a draw. Oro has magically sealed his other arm to prevent him from accidentally killing someone.
In the same vein as Gen, Fo Fai from Battle Arena Toshinden. Over a hundred, and still kicking it with kids 1/6th his age.
Psychic Force's Genshin Kenjoh definitely qualifies for this trope. Despite finding himself taking on young psychiccers who are able to either use fire, ice, or wind psychic powers, he doesn't yield or falter from within sight and that he battles against all threats through the use of his Shintomagic. The fact that he's also determined to save a young Shinto Miko named Shiori from the Big Bad and his minions proves his strong nobility and heart, so much that he ends up sacrificing himself to help revive and save her so that she can go live on and attempt to save the world from its current ruin.
Final Fantasy IV: Tellah may appear to be an old codger and have a pathetic supply of MP, but he was quite the mage back in his days — this is demonstrated in the fact that he knew (and forgot) almost every White and Black spell there is, and fully remembers them, along with Meteor, at far earlier levels than either of your other Black Mages can hope to learn them. The only shame, then, is that actually pulling Meteor out of his bag of tricks is his swan song. And then there's Fusoya, who actually knows them ALL, AND dispels Zemus's hold on Golbez and Kain in one transaction.
Also this game's incarnation of Cid. In the original game, he's 54 years old, and in Final Fantasy IV: The After Years, he's 71, which ties with Strago for oldest playable character ever. What are his accomplishments? Let's see: he invented the airship (duh), is a playable character relying on brute force and hammers, has a boisterous and loud personality, and...oh yeah, he takes a flying leap from an airship and detonates what appears to be a mini nuke in his hand in order to seal up a passage for the party. And in a week, he's back on his feet and fixing your airship again. Just to be thorough, he also has the greatest physical strength of any character, surpassing the martial arts master, Yang, while being a 71 year old man.
"But man, you fucking kids! Back in GALUF'S day, you didn't die from a single sword wound from a pretty boy! No sir! If you wanted to die, you had to go and find the world's most powerful black mage, who despite BEING a mage is wearing FULL ARMOR and WIELDS A SWORD, and knows all the most powerful spells in the game. And hell, just getting to him was a lot harder, too! You had to go through TWO worlds. And it was uphill in BOTH of them. And when you were finally AT that fucking mage, you didn't say "oh hey, stab me, it's a cut scene". No, you PUSSY, you FOUGHT him! And you kept fighting until your hit points were fucking negative ten thousand billion. THEN you can die, you cock-sucking youngin'."
In short, there's a damn good reason why his Crowning Moment of Awesome is mentioned across this wiki more than any other part of FFV. He's simply the coolest guy in the entire game, and arguably the franchise.
Strago from Final Fantasy VI proves to be an exceptionally powerful wizard in spite of his age, and his granddaughter is also a player-character. He is 10 years older than the above mentioned Tellah, and his first act as a member of the party is to charge into a burning building to rescue his adopted granddaughter.
Cyan. At fifty years old, he's nearly twice the age of any of the other party members, save Strago. His first act in the story is to single-handedly kill the leader of the Imperial siege of Doma, and then later to go on a Roaring Rampage of Revenge, fully ready to kill every last Imperial in their base before stopping..
Final Fantasy X: The only qualification that Auron lacks for this is his actual age. He's only 35 (technically, only 25 since he actually died 10 years before the game takes place). That's right, his own death barely slowed him down. Despite his relatively young age compared to most of the other examples on this page, he is still at least a decade older than any of the other playable characters and he certainly looks and acts the part in every other respect.
Final Fantasy XIII: Similarly to Auron, Sazh is notably younger than most of the other examples on this page, only being in his early-mid forties. Yet, he frequently complains about being the old man on the team due to all of the other playable characters being less than half his age.
Vanille and Fang are chronologically over 500. However, due to spending most of that time as Human Popsicles, they are still physically and emotionally in their late teens-early twenties, so the trope still fits in regards to Sazh.
Same place as Kliff Undersn from Guilty Gear, apparently. As a previous Commander of the Holy Order of Sacred Knights (at bare minimum 76 years old by the final battle of the Holy War, and he doesn't have Sol Badguy'senhanced longevity), he was an engine of destruction in his prime, being able to go toe-to-toe with Justice no less than seventeen times throughout the war and living through all of them, and holding off the advance of the Megadeth-class Hydra for a whole week, saving London in the process. Even as an old and stooped dwarf of a man, he can still expertly wield his Dragonslayer Sword and strike hard enough to easily stun people one quarter of his age and four times his size. His only limiting factor is apparently his back, which does give out from time to time.
Sol Badguy is possibly a literal example during the events of Guilty Gear II: Overture, as it's heavily implied that he's the biological father of Dizzy, and hence has a grandson in Sin.
Dynasty Warriors brings us Huang Zhong, easily the oldest looking character in the game, but a good swordsman and an amazing archer nonetheless.
Although Jia Xu is actually a year older than him. Similarly, although you can't tell because his model doesn't change, Ding Feng is eighty years old during Jin's final battle against Wu and still the most physically imposing character in the game (Meng Huo is as tall as him and probably heavier, but he isn't as obviously muscular).
Sister series Samurai Warriors, not to be outdone, gives us Yoshihiro Shimazu, who - despite being a craggy old man with the requisite white beard - is built like a brick outhouse and can swing around a giant hammer with ease.
Drachma from Skies of Arcadia. He's an old Captain Ahab expy who uses a freaking MECHANICAL ARM to fight, either by shooting the hand at the enemy, or running up and pimp slapping the enemy in the face. He's likely to be at least twice the level of any of the other party members at the time and will easily double the HP of any party member except maybe Vyse long after they've caught up.
Shujinko from Mortal Kombat: Deception. Over the 50-something year period in which the game takes place, he receives training from every martial arts master in the realms. Oh, and he can absorb the fighting ability of anybody he meets.
The End from Metal Gear Solid 3: Snake Eater. Sure, the guy's over a hundred years old, with about a week's worth of life left in him, but he's still the best sniper in the world. In addition, he can run faster then Naked Snake, is capable of photosynthesis, and is the absolute king of camouflage. He may be as old as the hills, but he will take you down. With tranquilizer rounds.
Really all the Cobras can count for this. You have to remember that they were already veteran soldiers when the group was founded 32 years before Snake Eater's events and by the time of their deaths were well into their 50s. The Boss is a slight exception since she is only 48, but she makes up for it in sheer badassness.
Old Snake in MGS4 is, this being Metal Gear, a deconstruction. While he's still one of the best fighters on the planet, his body is rapidly aging, resulting in reduced fitness and aches. He's not treated like an experienced soldier, but like an old man who gets way above his head with his mission.
Big Boss himself, who by the time of Metal Gear 1 was in his 60s and still considered THE most badass soldier of the century. By the time of MGS4, he's already survived being (supposedly) killed TWICE (the first time had his fortress collapse around him, the second involved being set on fire), was in a coma for about 15 years, had his body restored partially from the remains of his dead clones, and he was STILL considered to be THE badass to end all badasses. Also, he still scared Solid Snake when they had their little encounter in the cemetery. He was in his eighties.
As it turns out, his first supposed death was actually his body double Venom Snake being Killed Off for Real. That said, Venom in the first Metal Gear still very much counts; he's in his early 60s when he fights Solid Snake, but still gives the much younger soldier one of the toughest battles of his life.
Four syllables: CQC Hug.
Revolver Ocelot was in his sixties in MGS1, but that didn't stop him from being a badass 'Ricochet Genius' or handling his revolvers like he was still in his twenties. In MGS4 he's aged 10 years, and he's able to take Old Snake on in hand-to-hand combat. Twice.
Bill from Left 4 Dead may look like a nursing-home candidate, but he doesn't walk, talk, or shoot like one. He is, in point of fact, a former Green Beret who did two tours of duty in Vietnam.
"I was too old for this shit fifteen years ago."
He also is extremely close with the "kid" on the team, Zoey, acting much like a father or grandfather to her.
Literal example: There is a battle with Professor Oak in Gen I that was taken out of the final game. He uses Pokémon that are level 66 to 70, placing his strength above the player's rival and the Pokémon League Champion.
The Veteran class may count. They're all old men and women who, likely from the years of training, have Pokémon generally of higher levels than those of other trainers around them.
Drayden from Unova. In White he's a Retired Badass, but in Black, White 2, and Black 2, he's the Dragon-type Gym Leader. In Black 2 and White 2, Iris even refers to him as her grandfather, though they aren't actually blood relatives. It is mentioned that he wrestles with his Pokémon—one of which being Haxorus, a species that boasts one of the highest attacking stats in the game.
Special mention goes to the fact that Drayden wrestles his dragon pokemon to train them. Again, he considers wrestling dragons to be training... for the dragons.
Pokemon X and Y adds gym leaders Ramos and Wulfric to the list. The former, while only the 4th leader of the region, is said to make his way through his whole gym himself to his podium at the top. His gym being a climbing frame with climbing and swinging ropes. Wulfric, however is the final gym leader in the region.
Most regions have at least one gym leader that qualifies as one, such as Blaine, Pryce, and Wattson. Among champions, there's Alder, who's we find out is a literal grandpa in Black 2 and White 2.
Pokémon Sun and Moon introduces Drampa, an elderly Normal/Dragon type who goes berserk when it sees a child being hurt.
Pokémon Colosseum has Evice who is the old mayor of Phenac City and his team is one of the deadliest in the Pokemon franchise with a Slaking that gets Truant removed through Skill Swap, a Salamence, Scizor, Slowking, Machamp and his final Pokemon which is a Tyranitar. Due to this he is considered one of the hardest bosses in Pokemon history.
Heihachi Mishima from Tekken is improbably hardcore...not just incredibly strong and muscled for such an old guy, but also highly proficient at martial arts and he can generate electricity from his fists. And beat up 4 generations of his own family who tried to go against him. And he's incredibly rich and runs a world-spanning corporation. And he has a grizzly bear as a pet.
And you can then go one step further into the Mishima family tree with Heihachi's dad, Jinpachi Mishima. Had the family business taken from him, but chose to remain peaceful even though he kicks arse...then he gets possessed by a demon. Now he has blue skin, huge muscles, a gaping demon pair of jaws WHICH BREATHE FIRE in his chest, and has electricity always coruscating around him. That makes him a Badass GREAT Grandpa. Oh, and his goal is to destroy all of existence.
His son and grandson are both infused with the Devil himself and he can still take them down. And he can also take down an army of Jack-5's AND survive an explosion strong enough to level a mountain fortress AND survive for 5 months unconcious.
There's also Wang Jinrei. He's pretty damn old during his first appearances (in the first two games), but, by Tekken 4, he is well over 100 years old. And he still kicks ass.
And Olcadan. Both come from an age before Soul Edge was even forged and have never lost a single battle, and the only draw they have ever experienced is heavily implied to have been against each other.
Mitsurugi is headed towards this fast. With nothing other than being damn good with a katana, he's able to defeat any opponent in single combat, turn to tide of hopeless battles by himself, can block bullets with his blade, has only one confirmed loss in the series's 20+ year history and has to seek out opponents like Nightmare just so combat doesn't bore him to death. He's in his fifties.
Ammon Jerro in Neverwinter Nights 2. His age is indeterminate but he's at least old enough to be the thirty-something Shandra Jerro's grandfather (or great-grandfather, or great-great-grandfather; Shandra isn't sure). And he's definitely a badass: he's the warlock in the game's intro, going toe-to-toe with the King of Shadows. He's also a very powerful warlock in his own right (insofar as the game's rules can let a warlock be powerful).
Ezio Auditore. It's most prounounced in Revelations, where he holds off armies and leaps around like he's still 17. He's 55. In the 16th Century!
Altair as well in his segments, where at the age of 60 he's still at least capable of free-running. While Ezio lived to be 65, Altair lived to be 92 in the 14th Century. He even lived to see his own son Darim become a Badass Grandpa as well. Even one of the later segments, when Altair's age is clearly taking its toll on him and he can no longer run or climb and he occasionally goes into coughing fits he makes up for his physical infirmity with the upgrades to his gear he invented by studying the Apple like the second Hidden Blade and the Hidden Gun, and when he has the legion of Masyaf Assassins against him he can turn each and every one of them to his side just by disarming these young, fit, trained Assassins of their weapons...At 90 years of age.
J from Castlevania: Aria of Sorrow spends most of the game wandering around as an amnesiac. He's at least fifty years old, and honestly, doesn't seem like he can do much. Then right before you get to the final boss, he's standing in the doorway. With Vampire Killer. And you've recently found out Soma Cruz, the main character, is Dracula's reincarnation. This is when he reveals he's in reality Julius Belmont, last in the line of very, VERY successful vampire hunters. Oh, guess what you are. Belmont charges, and you realize all of a sudden you are about to be in a universe of hurt.
The sequel features Julius getting beaten by Dario because Dario can use the dark seals to regenerate. This is because Julius can't use seals, whereas Soma has learnt to for the bosses. However, the badass part is that before then Julius was killing regenerating enemies before they had a chance to regenerate. Even Soma notes that should be impossible.
If the player dawdles long enough, he can become a Badass Grandpa in Fable I. The ancient hero Scyth is also supposedly pretty badass.
Jolee "I'm Too Old For This" Bindo from Star Wars: Knights of the Old Republic. When you first meet him, he goes four-on-one against some of Kashyykk's native predators. And wins. Without breaking a sweat. Also, he's a Jedi, and old and respected enough to walk out on the Council without consequence.
Kreia from Knights of the Old Republic II: The Sith Lords, who serves as a rather morally ambiguous mentor to your character after having already been a Jedi Master and a Sith Lord. If that's not enough, her ultimate purpose is equally badass: she wants nothing less than the death of the Force itself, so people will stop being so weak and dependant on it. You're the key to making it happen, and she will remove any obstacle or inconvenience to her plan.
1000 years prior to the setting of Fire Emblem: The Blazing Blade, eight legendary heroes cleansed the land of dragons. Two of them are still alive, and still the most powerful beings on the continent (one of them becomes playable for the final chapter and is the most powerful character you ever get, but the other one outdoes him by bringing a dragon back to life, complete with its original soul. The Big Bad qualifies, also, having been an old friend of one of those two some 500 years previous before a differing in opinions led to his turn toward evil.
Dheginsea the Black Dragon King from Fire Emblem Tellius. Throughout the two games, he's portrayed as an exceptionally stubborn old man who wouldn't budge from his neutral position no matter what, just so he doesn't break his covenant with the goddess Ashera. He made a promise to not start or fight in any war, which certainly makes him seem like just an old, bitter scalebag... until the goddess herself calls upon him for help against her sister, Yune. It's only at this point where you realize that Dheginsea is a gigantic black dragon capable of destroying your whole army with utmost ease. In the game, normally each class would have one or two stat that can cap at 40, but Dheginsea? He has Strength and Defense capped at 50, and a HP of 100 (where your units with the highest caps will have a max of maybe 80). Not only that, he has Mantle, a skill which nullifies critical attacks, makes him invincible to anything that's not blessed by Yune, heals him the amount of luck he has (30) every turn, and nullifies any skill you might have. And then he has Ire, which randomly enables him to deal 3x damage. Oh boy... It's worth mentioning that he's probably over 2000 years old.
Anduin Lothar from the Warcraft series. He formed The Alliance and led it to victory while in his sixties.
Cairne Bloodhoof and (according to some accounts) Prophet Velen.
The Tauren Chieftain multiplayer hero shares it with Cairne - while they have some choices for names that are randomized, they complain about their old bones aching while having the highest amount of the strength stat compared to all the other ones, even the demonic Dreadlord (plus creating shockwaves by swinging their axes and stomping the ground...).
Cairne was 97 during Warcraft III, so about mid 80s in human years
And despite his age, Cairne was still able to put the smackdown on Garrosh for awhile anyways...
High Overlord Varok Saurfang (yes, THAT Saurfang) who is at least in his late 60s (I don't really know how orcs age but read that Thrall was in his twenties in Warcraft III so I am guessing Saurfang's age on how he looks) and still can one-shot anyone with cleave and puts Chuck Norris to shame with his awesome.
The Alliance were getting Genn Motherfucking Greymane.
Tirion Fordring. TIRION FRIGGIN' FORDRING. When the Lich King states outright that he is going to recruit you whether you like it or not and your sheer strength of faith is enough to not only cleanse a cursed corrupted sword that's been that way for YEARS, but also bust the tiny glacier immobilizing you so you can break Frostmourne with the same sword...you know you're a badass.
Gogen from Arc the Lad: 3.000 years old, already survived one apocalypse and spent most of his time sealed with the big bad: during his first appearance in Arc II he litteraly blows up the game's equivalent of the Statue of the Liberty with one spell.
Daitetsu Minase from Super Robot Wars Original Generation. Has a six year old graddaughter, qualifying his on the age front. On the Badass? Well, he survived getting blown the fuck up by the Granzon mecha (whose weaponry can warp dimensions), commanded a single battleship against some crazy odds involving submarine warfare, facing off against an enemy force by himself twice (first time against six submarines, second time against the combined forces of the Divine Crusaders at Aidenous while his crew were beating the piss out of Bian Zoldark's Valsion), and has served as captain of two battleships that he kicked major ass with in both the first game and the anime adaptation.
In the second game, he gets many Big Damn Heroes moments, and at the risk of spoilers, manages to get his troops to safety after Operation Plantagenet goes awry, and flips a massive middle finger in the form of a massive energy blast at the enemy troops simultaneously.
Super Robot Wars has a whole bunch of those, for example Master Asia (the grand-daddy of badasses from G Gundam), Master Rishu (he trained The Sword That Cleaves Evil, and he's still good for a fight) and Alpha 3's Baran Doban.
Wess from MOTHER 3 is probably the most powerful and helpful Nonplayable party member in the game.
Two words: Master Xehanort. Good fuckity God. The guy's a bald, bent, skinny old man who might just be the biggest Badass out of Sora, Riku, every other Xehanort, Organization XIII, Mickey Mouse and Sephiroth. This is really no exaggeration. Behold.
Also, Xigbar. First Organization member you fight upon entering the castle, only Nobody with visible age lines and graying hair, has an Eyepatch of Power and shows that he's been watching by eliminating every heartless facing you in about five seconds. THEN he reveals that he knew the previous Keyblade Masters and you don't match up to them at all. Yeah, you beat him eventually. But he doesn't go down easily.
Not exactly an old man but has the same "must be good or else he would be dead" pre-requisite. Namely the Demoman from Team Fortress 2
"What makes me a good Demoman? If I were a bad Demoman, I wouldn't be sittin' here, discussin' it with you, now would I?!"
A straighter example is Gray Mann, with his first appearance (in the comics) having him sneaking into a room where his two brothers are and casually stabbing two Engineers in a way that mimics the Spy, and then he adds the most famous line of the Spy.
There's also the Medic, who seems to be the oldest of the mercenaries, with hints scattered throughout the game that he was a young field surgeon in the German Wehrmacht during WWII, which would place his age bracket into the early fifties to mid-fifties during the time frame of the game (1968-1972).
And the Soldier fought (sort of) in that very same war.
Radigan Conagher, mechanical genius, possessor of Hot Blooded Sideburns, became even more Bad Ass after he came in contact with Australium. Exhibit one, Radigan with a robot hand and chest hair in the shape of Texas. Also actually a grandfather (to Dell Conagher, the BLU engineer).
Heavy is heavily implied to have been a young boy in the early Stalin era, making him in his late 40s at the very least.
Engineer's father is implied to have participated in Team Fortress Classic, which takes place in 1930 in this timeline, and a picture of the two suggests that Dell was about 10 at the time, putting his birth year somewhere in the 1920s.
Cidolfas Orlandu of Final Fantasy Tactics, the "Thunder God" himself. The leader of the Nanten Knights and a general within the ranks of the banner of the Black Lion of Prince Goltana, he defects to Ramza's (you) forces because he realizes that despite having served the house of Goltana for decades...the war the Prince is esclating against Duke Larg for the crown will tear Ivalice (the games' setting) apart. Right from the moment you see him, even though he's among the ranks of many of the games' antagonists...you know he's honorable and awesome, daring to question his liege' intentions. You realize from reading his profile that he can probably do this because no one would stand a chance against him if they felt then need to quiet him...as is displayed later in the game. No martyrdom for this undefeated swordmaster! Oh no, he joins you after that and subsequently breaks the game because he's so damn powerful...the need for your other party members becomes tertiary. He has every major sword ability in the game including one that heals him while still doing massive damage, he comes with Excalibur, and he has superior stats. He IS Ramza's army by the end. If you can actually lose with Cid on your team then you...you just suck.
Technically, your whole party can become this. The game keeps track of the date and moving between each space on the map takes one game day. The game asks for Ramza's birthdate at the beginning and when that date passes, Ramza gains a year in the character biographies page. This happens for every unique character. It doesn't affect the story or abilities in any way, however.
Tenchu 2 had Master Shiunsai and...Urano Takehito.
Father Paul Rawlings from Clive Barker's Jericho is a combination of this and Badass Preacher. He's 67 years old, wields two pistols effortlessly in combat, is a powerful exorcist, takes no nonsense, and has Seen It All to the extent that he's barely even fazed by the supernatural terrors he faces.
Gen Fu from Dead or Alive. He may be in his 60s, but that man can kick some ass.
He also overlaps with Cultured Badass as some of his attacks suggest. Catching a woman in freefall and setting her down gently after kicking her into the air first? Very noble.
Some of the Capos and Underbosses in The Godfather: The Game are clearly old men with heads full of grey hair, but they're every bit as willing and able to kick your ass - or, if they're Aldo's Corleone brothers-in-crime, help him kick ass - as their younger underlings.
Master Li of Jade Empire fame. He's your tutor in the martial arts, and when a weird evil-lookinng bloke turns up in your village on a ship, Master Li arrives and jumps onto the ship, punching it so hard that it sinks. Then you find out he's actually the Emperor's brother, Sun Li the Glorious Strategist- and boy, does he deserve that title. Just after you kill the Emperor (did we mention he is, at that point, powered by a God?), Sun Li kills you. With a single punch. This is his way of telling you that he's been playing you right from the start.
It's rather relative to species in Mass Effect. For example, krogan can live over a thousand years, and Urdnot Wrex is old even for one of them. He's got the battle philosophy of a seasoned old wardog, and is packing Biotics to boot. There's also Mordin, who is 38 (approximately 88-ish in human years). Most salarians don't live past 40, and looking at his face you can see the wrinkled, dry skin and numerous injuries.
Asari have a stage of life devoted to this; Matriarchs are explicitly stated to be some of the most powerful biotics in the galaxy. In the second game, your asari squad member, Samara, is technically a marginal case of this trope: she hasn't entered the matriarch stage of her life, so she's probably only middle-aged. That said, she can devastate much younger opponents, and you can level up her class ability to the point where her biotic power is equivalent to a matriarch's. One can only imagine what she'll be capable of when she actually does reach matriarch status.
Detective Badd in Ace Attorney Investigations. He wears a trenchcoat pockmarked with bullet holes and is the only person to sucessfully dodge Franziska's whip. By the final case of the game, he's over sixty years old but still manages to keep up the Yatagarasu tradition on his own, where previously the job was done by three people, plus his dramatic *Click* Hello to Shih-na when she takes Kay hostage.
Zeus in God of War. He looks like an old man, but is still more physically imposing than Kratos. When you fight him at the end of the game, Kratos has a half-dozen weapons, including a supposedly-ultimate weapon called the Blade of Olympus, and Zeus is still a tough opponent even though he's only using his bare hands for most of the fight. And towards the end of their fight in III, Zeus officially quits screwing around and unleashes his full power, overwhelming Kratos completely, and at that point would have killed him had Kratos not used the power of hope.
Cassidy of Fallout 2. Of all the recruitable NPCs, he is arguably the most helpful in a fight, with enviable amount of experience using small arms, melee weapons and unarmed combat. He's well into his 60s and suffers from a heart condition that prevents him from taking combat drugs, but considering how good he is to begin with there's not much reason to try.
Fallout: New Vegas has the Enclave Remnants, former members of The Empire from Fallout 2. While it's been a long time since the fall of Navarro and all of them are probably in their sixties at least if convinced by The Courier to participate in the final battle for old time's sake will prove that even now they can still be utterly deadly in combat (especially if you're wearing Power Armor).
Joshua Graham, AKA the Burned Man. While his age is never outright stated, as the co-founder of Caesar's Legion he would have to be in his mid-fifties by the time of the game. He's considered one of the biggest in-game Memetic Badasses renowned for surviving almost anything, be it the NCR's elite snipers or being burned alive and tossed down the Grand Canyon.
Independence War 2: Edge of Chaos has Lucrecia Johnston. While she's dead by the time the game begins, she was apparently a Space Pirate in her day with many followers, even having set up an elaborate base of operations capable of constructing ship parts at a molecular level and receiving communications without giving away its position, among other things. Cal Johnston is impressed to learn this side of his grandma's life, to say the least (his recently murdered father was just a miner trying to make an honest living who presumably wanted the same for his son), and it's even lampshaded by his fellow escaped inmates when they see the base for the first time.
The Chinese explorer in Age of Empires III is an aged Shaolin master armed with only his bare fists.
Ford Crueller from Psychonauts. Before he retired, he was known as one of the greatest Psychonauts in the world. He can't help you much (because a psychic injury fractured his mind, making him senile when he's away from Psiantium), but he still manages to show up to help Sasha and Milla battle Oleander, a huge hunk of Psiantium tied onto his back.
Landon Ricketts from Red Dead Redemption certainly qualifies. Not only is he someone John Marston somewhat looks up to (for being famous back in the day), but he teaches you the third level Dead Eye aiming and keeps pace with you for a few missions.
It gets better in Red Dead Redemption: Undead Nightmare. There are three towns in the game that will NEVER come under zombie attack. Two of them are fortresses with tall walls and only ladders to access it. The third? A brothel in Mexico with no tall walls. Landon Ricketts is single-handedly keeping the zombies down in Casa Magruda with nothing but his trusty-six shooter. He also has the idea of combining the zombie bait and dynamite into a weapon that draws the zombies in before blasting them into red mist.
McBain in Legend of Heroes V: Song Of the Ocean. Sure, he's a troubadour, but he's a troubadour who can punch through solid rock. At age 62. And, while Forte is the designated protagonist, it's really McBain that is leading the party to save the world.
Valkenhayn R. Hellsing from BlazBlue is a werewolfbutler working for the Alucard family who also happens to be one of the legendary Six Heroes.
Sam Fisher of Splinter Cell is practically an embodiment of this trope. Let's see what's on the menu! A S.E.A.L vet? Check. Capable of taking down numerous Special Forces operatives more than half his age? Check. Can and WILL take these operatives on without a weapon? Check. A fan of the Jack Bauer Interrogation Technique? As every victim knows (assuming they're still alive), check. Oh, Dear Lord, check.
Colonel Victor Hoffman from Gears of War definitely qualifies. In world where almost 99% of the human population has been killed off and average life expectancy can't be far past 30, Hoffman is canonically 60 years old at the time of Gears of War 3. Despite being almost twice as old as the other player characters, he hoists heavy machine guns and rocket launchers easily. His character is essentially R. Lee Ermey plus 100 pounds of muscle.
As of the fourth game, Marcus himself has become this. He might be older but he's still just as huge and combat-capable.
The Elder Scrolls V: Skyrim has the Greybeards, monks who live up in the Throat of the World (the highest mountain of Tamriel) who have mastered the Thu'um. To put things in perspective, most of them don't talk because if they did they'd take out half of the mountain they live in with their voices. That's how powerful their Thu'um is.
A possible encounter out on the roads is against an Old Orc who seeks an honourable death in battle rather than wasting away in a bed, and he can't just commit suicide as it would displease his god, Malacath. He'll be surrounded by the corpses of multiple sabre-toothed cats when you find him. Becomes a Dying Moment of Awesome if you've been identified as the Dragonborn and have completed Malacath's daedric quest, as it means this Old Orc gets to die in fair battle against a legendary dragonslayer who is also the chosen champion of his god.
[PROTOTYPE 2] has Dr. Koenig. At first, he just seems like a regular Mad Scientist working for Blackwatch. He's easily pushing into his 70's, looks like a typical frail old man and speaks like a kindly grandpa. Then he proves he's not quite such a nice grandpa after all. He successfully manipulates both Heller and Blackwatch into helping him with his goal, playing both sides against each other until Heller gets wise to it. And this is before his arms turn into guillotines.
Anarchy Reigns has Douglas Williamsburg whose stats says that he might be 180 years old. That doesn't prevent him from kicking a lot of ass though.
Rowen J. Ilbert from Tales of Xillia. He's the oldest playable character in the Tales Series, and a Battle Butler who's also a war veteran. He doesn't take his master's kidnapping sitting down, to say in the least.
There's not one Badass Grandpa, but TWO of them in Chrono Cross. Radius and Viper.
Joel, from The Last of Us is over 50, but works as a smuggler, and regularly beats both zombies and people to death with his bare hands.
Old Peppy Hare, senior member of the Star Fox team. As a member of the original team from the backstory, he's a full generation older than the rest, but still kicks ass in an Arwing.
Gaza, in Legend of Legaia is one of these. 61 during the game, a feared warrior deemed nigh unstoppable by soldiers in Conkram when you travel back in time 10 years, and by far the strongest being in the game who isn't wearing a Serunote Or is one, in the case of Rogue or Tieg
Bola and Klaymoor from Megaman Legends 2 are old enough to be retired and Klaymoor flat-out has to retreat when he puts his back out during his fight. They're also the only two human bosses you fight who rely on powered armor rather than piloting Humongous Mecha and are every bit as big of a threat as, say, Tron in her massive crab robot.
In Jaleco's Psychic 5, Genzoh, at age 88, is older than the other four Espers put together, yet still has the highest Hover and Attack of all.
Monomachus of Tears to Tiara 2 sports an long white beard. And he's still one of the strongest soldiers in ex-empire, going toe-to-toe with Golyat and taking down a huge number of mooks and a kraken in his Last Stand.
For the uninitiated, S.T.A.L.K.E.R. is set in an alternate universe Chernobyl where reality itself is off it's meds and it's populated by freakish mutants. The Red Forest is even by the Zone's standards a scary, dangerous and foreboding place, where the craziness and horror is ramped Up to Eleven and highly trained Stalkers only dare make excursions into it in large groups with plenty of military-grade hardware. This is really something that needs to be explained to that old man who lives in a shack in the forest by himself, with only a ushanka and a break-open hunting shotgun for protection. Oh, and he bags a bloodsucker, which is basically a mutant Cthulhu vampire which can turn invisible, eats entire clips of assault rifle ammo, and probably urinates high-octane Nightmare Fuel.
Frank Patterson from Nosferatu The Wrath Of Malachi. He carries around a machine gun in his trunk. And his family photo shows him standing atop the carcass of an animal waving the gun in the air triumphantly.
100 years after the First Doom Island War, the first reaction from Guy in Lufia & The Fortress of Doom is to prepare to fight the Sinistrals. Unfortunately, even getting himself worked up turns out to be too much for him.
Randolph in Lufia: The Legend Returns is an elderly white-beared man who serves as a Princess's bodyguard. Did we mention he's the party's dedicated BFS user?
Overwatch: Both Reinhardt and Torbjörn are pretty old, at 61 and 57 respectively but they're still kicking ass and taking names. Soldier: 76's age isn't known but he's obviously up there in the years too. Ana counts too as a badass grandma when it is announced that she will be playable, as she's 60 years old, the second oldest character in the game (only Reinhardt is older than her).
Among your travels in Bloodborne, you will come across Father Gascoigne, Eileen the Crow and Retired Hunter Djura. They're all old, but when you fight them (the former's a mandatory Boss Fight, but the latter two are Bonus Bosses), they will destroy the unprepared and will make even the experienced take a few tries to down them properly. And that's not getting to Gehrman, the First Hunter.
Evolve: Griffin is referred to as an old man by both himself and other hunters, but he's had more practice hunting and killing xenofauna than anyone else on the team and he's still going. Lennox, while similarly aged, doesn't have his years of experience. What she does have is four tons of armor and weapons in Mini-Mecha form and the desire to beat the living hell out of the monsters that destroyed her colony.
Everyone in Earthsiege. According to the backstory of the first game, the Robot War that erupts missed a tiny museum loaded with antique HERCULAN robots and equally old staff consisting of former techs and pilots with an average age of 67. The most iconic is your Mission Control, Ambrose Gierling, a cantankerous old former HERC pilot and blatant George S PattonExpy played by John Rice, who easily looks the part of a 70-year-old war veteran.
Xenoblade Chronicles X has both Bozé Lowes and Kentaro Nagi, respectively 54 and 57 years of age. They both have long military histories and still kick just as much ass as the younger party members.
Bozé: I may be older, but I can still pull my weight.