It seems to be widely accepted in the medical profession that the younger you act and the more you continue to challenge yourself mentally, the "younger" and more able you remain. Certainly, I observed in my grandparents that as soon as they "gracefully accepted" old age they rapidly went downhill. Fortunately both my parents observed the same and they continue to remain as active as possible.
If my Dad (80-something now) was at all interested in regaining the flying licence he held back in the 40's I'd be very willing to help him out with a big proportion of the cost, even if he never intended (or perhaps was medically able) to fly solo. It's much cheaper and much better value than spending the money on an old people's home.