He's an Old Soldier, all right—a very old soldier who is adamant he's Made of Iron and good for another battle, even though it's woefully clear that said iron is showing a lot of wear and tear and his fighting days are behind him.
To fit this trope, the subject must be far too old and feeble to do battle anymore, or perhaps seriously disabled (either from previous battles or illness), or both. The subject must also be in denial and insist they're good for another round. Remember: Perilous Old Fool.
Quite often, did have a well-earned badass reputation way back when, but has suffered some very literal Badass Decay. Very often ends up with a bad case of dead, and Curb Stomp Battles are pretty much the norm.
If the soldier is willing to sacrifice himself because he's old and infirm and the others have their lives ahead of them, or knows he's too old for a fight but wants to go out in a blaze of glory, that's Death Seeker — or More Hero Than Thou — not this trope. If they're going to die anyways and decide to fight to the last breath, that's Face Death with Dignity and possibly Taking You with Me. If someone's old as dirt but still has the chops, that's an Old Soldier, Old Master or whatever and should only be listed here as a subversion if they're believed to be this. Definitely related to (and possible Sub-Trope of) Too Dumb to Live and Fearless Fool.
- Archie Comics: One comic shows several veterans chasing a thief — but they no longer have their youthful stamina. The thief even says "This is where I lose the geezer brigade".
- Batman: Batman being aging, worn-out and past his peak is a recurring theme in the comics. Batman: The Dark Knight Returns has Batman tries to fight a (much younger, stronger, and faster) leader of the Mutants on his terms and ends up battered and with a broken arm. For the rematch, Bruce accepts his age and fights the way an old man should fight a young upstart: by choosing the battlefield to his advantage, using precise, practiced techniques to disable the opponent — and avoiding direct brute force stand-offs.
- Mulan: Subverted; Mulan's father is aware that he is not in the best condition to fight, but is willing to die for his country and honor. Naturally, Mulan doesn't find this acceptable.
- The Dark Knight Rises: Bruce is only in his late thirties to early forties, yet his accumulated injuries mean he is not nearly fit or strong enough for his first fight with Bane. Alfred also accuses Bruce of being a Glory Seeker by returning as Batman when he could be more effective by using his other resources like his technology and money to help the police, and worries that Bruce's insistence on being Batman amounts to an extravagant form of suicide.
Bane: You fight like a younger man: with nothing held back. Admirable... but mistaken.
- Independence Day: Russel hasn't been in a fighter plane since the Vietnam War, but he wants payback for having been (supposedly) abducted by the invading aliens. He contributes to the battle by making a Heroic Sacrifice just before the giant alien ship can use its Wave-Motion Gun on Area 51.
- Skyfall tweaks this trope a little. Bond is left pretty significantly disabled after his "death", in ways that seriously impact his ability to do all the things that make him James Bond. (No, not that thing, that's fine.) He's left physically debilitated, unable to shoot straight, and reliant on pills and liquor. But he's still sent back into battle despite failing all the assessment exams, even the weapons course and, being Bond, still ends up kicking the requisite ass, though he does need the assistance of two literal old people to do so.
- Silva: Medical evaluation: fail. Physical evaluation: fail. Psychological evaluation, alcohol and substance addiction indicated. Ooh! Pathological rejection of authority based on unresolved childhood trauma. Subject is not approved for field duty and immediate suspension for service advised. What is this if not betrayal? She sent you off to me, knowing you're not ready, knowing you'll likely die. Mommy was very bad.
- Ciaphas Cain: In one novel, a retired Imperial Guard veteran joins the militia to help fend off a Chaos invasion, and although he's very enthusiastic it's clear he's not quite all there.
- Discworld: Cohen the Barbarian is edging close to this by his first appearance in The Light Fantastic, with his bad back and lack of teeth, but once he gets his back straightened out and a pair of (diamond!) dentures, he returns to being a full-time badass.
- Heralds of Valdemar: Defied in By the Sword when a mercenary is left behind because he'd be tempted to take part in "one last battle", despite being very old and having only one arm.
- Legend is a subversion of this. By all standards of the setting Druss is way too old to fight another war and Death itself mocks him about it. He has crippling arthritis in his hands and his body is wrecked by decades of fighting. However, he quickly proves that he is still the deadliest man alive and still strong enough to kill hundreds of enemy soldiers in hand-to-hand combat.
- Myth Adventures: Ajax the Archer in Myth Conceptions is actually pretty badass in spite of being quite past his prime, but the fool part comes in given how hopelessly overwhelming the odds are: even if he were a One-Man Army he wouldn't be enough.
- Redwall: Bluddbeak, the redkite from Triss, is one of the Trope Namers. He has rheumatism. He's blind. And he's adamant that he's still the great adder-killer he once was and can take on a trio of the snakes who work together as one. Oh, is he wrong. The other "fool" Skipper is referring to in the quote is Ovus the owl, who feels the need to help Bluddbeak out despite his own great age and rheumatism. He fares better only in that he gets some Last Words and a decent burial, while all that's left of Bluddbeak are scattered feathers.
- Dad's Army: Corporal Jones, a veteran of wars going right back to 1886, who saw fighting in The Sudan (1886), South Africa (1899-1902), a bit of WW1 (1914-1918)... and who in 1940, aged 80, wants to come back for his fourth...
- Doctor Who: The Doctor thinks Brigadier Lethbridge-Stewart is one of these in "Battlefield", if his line over the Brig's unconscious (assumed dead) body is any indication.
- Game of Thrones: Balon's forces are far too inadequate to take on any of the various armies he's choosing to stand against, but he insists on striking it out by himself because he's too proud, selfish and stubborn to even consider allying with anyone else.
- In Gosei Sentai Dai Ranger there's the very high ranking Gorma leader, Archbishop Saw, who initially subverts this trope, being able to hold his own against the DaiRangers. During the mecha battle, his advanced age is apparent as he is too slow to hit Dairenoh and he's stunned for a surprisingly long time after getting hit, allowing him to be finished off. In his younger years, he may have wiped the floor with Dairenoh and survived its finisher, but as an old man, he's much less effective.
- A Key & Peele skit involves an army general hunting down a Retired Badass for what turns out to not be One Final Mission, but for a recommendation for someone who can do the job. The old retired soldier immediately starts insisting he's willing to come out of retirement for the One Final Mission, revealing himself as this trope by showing how out of shape he is while trying to show he's still got it. Eventually he's killed insisting he can still catch bullets.
- Star Trek: Deep Space Nine: In "Once More Unto the Breach", Kor is worried that he's being left out of the Dominion War and a chance to die in battle. Worf manages to have him assigned to General Martok's flagship. In the middle of a raid on a Dominion supply base, both Worf and Martok are injured, leaving Kor in command. At that moment, he starts to believe he is actually in the middle of a battle against the Federation nearly a century earlier, costing the raid at least one ship.
- Scrubs: In "My Brother, My Keeper", Dr Townshend (played by Dick Van Dyke) is an affable old doctor who is well loved by everyone, including Kelso (who hates everybody). But during the episode, he prescribes an "old school" procedure which goes disastrously wrong. Kelso confronts him about why he didn't prescribe a newer procedure, and Townshend admits he didn't know about it because he is too tired to keep up with medical advances, and is depending on his decades old knowledge. Kelso is forced to fire him.
- Dungeons & Dragons:
- This is the typical way for giff to die. Their culture has no respect for the infirm, so aging giffs will usually stay in active military duty, trying to prove they still have it. They can live to be 70, but few make it past 40 or 50.
- Goliaths have a similar issue. Goliath society is built upon competition and continually topping past achievements. Once a goliath suffers from a permanent injury or begins to lose physical ability due to age, they almost always die trying to do something that tops feats they'd accomplished when they were younger and healthier. This is noted as a serious issue for goliath communities, as it means they never have access to the wisdom that comes with age and experience and must always hope for leaders with innate wisdom, instead, while permanently missing out on leaders with experience.
- Metal Gear Solid 4 does the classic subversion — Snake keeps insisting he's able to fight, partly because he's a Death Seeker and partly because he is still able to fight out of sheer Determinator factor. However, he limps around in cutscenes, is missing half his face and has developed some form of lung disease from what had been badass smoking when he was younger.
- Overwatch: In terms of actual gameplay, Reinhardt Wilhelm is still a formidable warrior, but some of his emotes, along with the lore revealed in his comic, suggests that he is fast approaching this trope. He's absolutely committed to being a Knight in Shining Armor despite his advancing age and increasing physical degeneration (played for laughs in the in-game emotes where he throws his back out), and it's implied that he can't cope with the idea of laying down his arms and would prefer to fight until he dies.
- Ace Combat 7: Skies Unknown: Mihaly A. Shilage fits this trope to a T. A man his age should really not be flying fighter jets anymore, but Mihaly insists on doing it anyway. Every time he goes out on sortie, he comes back in a pretty bad shape due to the extreme strain being put on his body. When he meets Trigger, a younger ace pilot who proves to be a Worthy Opponent, he orders his wingmen to stay back and deal with Trigger himself out of pride, even as he's straining himself to the limit and is breathing heavily from all the high-G moves. His pride becomes his undoing as he ends up getting shot down in his final encounter with Trigger, and he ends up getting crippled for the rest of his life.
- The Legend of Korra: Lampshaded and subverted by Toph. She's the greatest earthbender in the world, but she's also 80-plus and her back is killing her. Sometimes you just gotta let the kids win the war. This is also the reason Katara never showed up for the Water Tribe Civil War.
- In the first episode of Batman Beyond, Bruce was still shown to be fighting crime into his old age, to the point that he suffered a heart attack during his last solo rescue mission. It wasn't even this that convinced him to hang up the cowl; rather, on the verge of being beaten to death by an opportunistic criminal, he drew a discarded gun in a moment of desperation, and his realisation of this after the fact is what got him to stop.
- Several veterans of the Boer War wanted to fight in World War II, being turned away because they were too old. There was one case where the man in question dyed his hair—but the heat made the dye run, revealing his gray hair and thus his age.
- Theodore Roosevelt wanted to fight in World War One also, but was likewise refused a commission by President Wilson. In this case it probably had far more to do with Teddy's status as a former President than his age.
- At the outbreak of World War I, Anatole France, a French writer, presented himself at the enlistment center, aged 70.
- King John the Blind of Bohemia died at the age of fifty because he insisted on fighting in the Battle of Crecy on the French side despite having been blind for ten years. Upon hearing that his son was probably engaged in combat, he told his companions to lead him into the fighting so that he could strike one blow with his sword, which they did by tying his horse to theirs. When the battle was over the king and his men were all found dead, their horses still tied together. A popular but incorrect legend says that Edward the Black Prince took his motto "Ich dien" ("I serve") afterwards as a tribute to the King of Bohemia. It should be noted that he was blind for a decade, his health was rapidly falling, and he was probably just very intentionally seeking Dying Moment of Awesome.