An actual old protagonist. Not an old man who becomes a teenager and acts like a teenager, but someone who has gone through the hardships of life. If he stays old, that's a plus. It would be something different to the norm. Thank you!
at what age would you consider old?: The Old Man Who Got a Second Round in Another World (50) Ossan (36) Ga Idol Ni Naru Hanashi A Certain Middle-Aged Man’s VRMMO Activity Log (38) Boukensha License o Hakudatsu Sareta Ossan Dakedo, Manamusume ga Dekita no de Nonbiri Jinsei o Oka Suru The Demon Lord’s Second Marriage
https://www.novelupdates.com/series/everlasting-immortal-firmament/ The MC is not the strongest, but he practically outsmarts every cultivator stronger than him with his experience and schemes.He's A genius merchant, someone who can make gold from dirt. He Started to cultivate after his 30's, an experienced and wise old man.
Try this if you want: https://www.novelupdates.com/series/superstars-of-tomorrow/ Old MC who died in apocalypse era, he reincarnated in teenager body. He didn't change his persona and still like an old man inside (other people thinks he is like an old man). He got along with his grandparents and other old person. He treats the descendant of his apocalypse friends like a child (eventhough outside they are on the same generation)