Retro Gaming

Heihachi Mishima of the Tekken series was old. I think 70s, but that probably varies based on the title.

EDIT: I guess he was only 52 at the time of the first Tekken, but he was 73 during Tekken 3. Though he was playable, he was also an antagonist, so, eh.

Can't remember many either, specially when ignoring characters like Alucard, that don't seem to have the archetype of an older individual, be it emotional or physical, despite the character's actual age.

Now, the few cases of older protagonists I can remember:
One Strike, if you consider games with a simulated old style, has an older playable character among the roster of characters.
And though also not an old game, but heavily inspired by Castlevania 3, Bloodstained: Curse of the Moon has an elderly playable character, and his play style reflects that.
And one of Gunbird's playable characters is also an elderly individual, and... (spoiler)

spoiler

in the joke ending, he even wishes to be young again.

Dunno if that'd be too young, but Gall Gruner from Tales of Heart, which according to the wiki is 45 y.o., does give a strong "older person" impression throughout the game.
Final Fantasy IV and V have older protagonists too, and in IV specifically, the character's age plays a role in gameplay.

Idk what you precisely get as retro and how much level of aging you want, but:

• Ezio from Assassin Creed is in 3 games where he starts in his 20's and at the end in 50's.
• Geralt is around 94 in Witcher 3 and sure as hell sometimes behave like a cranky old man, topic of age also often came in talks especially with Vesemir.

Not protagonists but prominent characters:

• KotOR have Canderous Ordo who is at least 40 and Jolee Bindo who looks as he's in his 60's but might be older. Also Kreia in KotOR 2
• Mass Effect have: Zaeed - in 40's and playing the part of old grizzled veteran, Liara - around 100 but as Asari barely an adult, Samara - 800 so entering old age for Asari, often mentions it, Thane 39, so while not particularly old for his species old for his job (assassin), Mordin - in his 30's so very old for Salarian and this topic comes often, Wrex - over 1000 so ancient for a Krogan and plays part of the grumpy old man
• Planescape Toment, Dak'kon is old and that is mentioned. Protagonist of that game is also very old but due to amnesia and copious amounts of magic it's not very relevant.
• Dynasty Warriors have some old playable characters like Zuo Ci, Huang Gai or Huang Zhong
• FF10 Auron is in 30's but behave like he was much older

not quite retro but all I can think of is Sazh in FF13

Mystic Towers! https://youtu.be/nUkRQxqBWNk?si=0eChDb0BT_dNq9ST

I actually saw this post yesterday but couldn't think of a good reply at the time lol