I think ageing - both physical as well as mental - are just an exercise in Newtonian Motion. Bodies at rest tend to stay at rest, bodies in motion tend to stay in motion. Minds at rest tend to stay at rest, minds in motion tend to stay in motion.
You need 3 things to make/keep your body healthy:
a) food
b) fresh air
c) exercise
I moved away from full on sparing in my late 30s, and focused my martial arts training (which was my way of keeping fit) on just doing the katas I was taught and work on perfecting the forms in the mind as well as the body - really moving all of it much closer to Tai Chi than martial arts. I still ski, and I still ski hard slopes, but I quit doing the moguls in my 30s, quit racing by my 40s, and now I just kick back and get into the zen of it. Being one with the mountain and not having to be the first one down, or King of the Hill and all that. But it's about the physicalness of it as much as being out in the snow and sun and fresh mountain air and the most mind-blowing beauty of being over Lake Tahoe If you do nothing, take up Tai Chi, its the best exercise program for old people ever. Really, billions of old folks in China and the US can't be wrong.
Bikes are good if you do it all the time, and hiking, particularly over terrain like up the side of Mount Hood a little bit or something. You do live in just about the greatest hiking area of the world there Virgina Marie. Get some good shoes (I think there is a company right there in Portland makes shoes just for that) and start walking. A lot of the people on this board, who've lived in one place most of their life, have a hard time imagining how beautiful it is to hike in the area you live in, how lush and deep the forests are, how rugged the coast line is, how the mountains dominate the horizon. Hell, I think its beautiful and I spend my life in SF and Sonoma and Marin counties, that's how awesome it is up there. You can hike around one of the most recent volcanoes in the world, how cool is that?
For your mind or my case what's left of it, puzzles/thought games, reading/writing and conversation seem to make all the difference. Playing cards is great because it's a puzzle thinking deal, and its conversational as all get out. Do crosswords or Sudoku. Talk to people.