That brings us to exercise, which is a great thing if you can enjoy it. Easy exercise, e.g. walking, shuffleboard, kite flying, billiards, ping pong, swimming, gently aerobic exercise machines, dancing, shuffleboard, golf, dog walking, frisbee, gardening, or just sharing simple activities with active younger relatives, are fine, and as little as 45 minutes on most days may be optimal.

I'm retired a few years and just a bit younger than your father, and I would spend 40 hours a week on those two kinds of activities except that my wife often direct otherwise, which I also enjoy considerably. Life is very good for me now. I have gotten rid of a vast majority of my programming and software books and almost eliminated programming activities entirely. The problem with programming is that if you like it, you always have a program that needs one more tweak, and that means that every day you will sit down much more than you expected to. Better to keep an active mind in an active body.