I've been away helping put Gramps (that's what we call my grandfather, with great affection) in a nursing home. If ever there was a case for staying active mentally and physically, he is one. Do the crossword every day (preferably the NY Times), run, walk or ride your bike whenever you can. There's a poem here somewhere, but I'm not sure if and when I'll be able to write it.
On the up side, it was nice to see the family (six days was perfect). My nephews are getting to be at that really fun age between 6 and 12, though I have high hopes--perhaps unrealistic--that "Uncle Pete" will still be cool when they're teenagers.