As I approached 65 I began to think of how much longer I wanted to be active (read: go into the mountains and go deer hunting) and I decided that 20 more years wouldn't be unreasonable... IF I shaped up. 4 to 5 mile daily walks were helping, but not quickly enough. The bike give me that extra little edge, both mentally and physically.
2 years ago when I picked up my bike, used for $30, and started short rides it was a little scary. I didn't have the control I remembered from my youth and I fell a couple times. Made me think again. But I pushed on and now can go down ''the scary hill" at speed that I was really afraid of 2 years ago. So mentally it's maybe been just as important as physically.
And it helps me set goals: a 25 mile ride next month, 10 miles at 15 mph. (both close), and a metric century next year would be nice.