my dad is 76 for example and he is mentally and physically more fit than most 20-30 year olds. He does logical puzzles a few hours a day (dont know if there is an english term). Every week he cycles a 50 km trip (2+ hours one way, 2+ hours back) besides his daily cycling and walking. And he is always looking for projects around the house, big ones, like you visit and suddenly half a wall is missing, and he decided to relay the electrics). Last month he put in new carpet in the entire house himself. 200m² he had I think. One night he couldnt sleep and did it at night at 3.30am haha.