I think this used to be much more common in the past. My grandfather, a farmer, also worked till about 6 months before passing, when his heart started weakening, at age 92. He would pull 12 hour days, and that's what kept him alive and happy. He would get depressed when he came to visit us in the city with nothing to do. Going from working 40 hours a week when you're 64 to idling all day as you turn 65 is just not healthy.