I just got started bicycling again after more than 20 years. I'm well over 50 and bought myself a legacy-style Schwinn 7 speed -- mostly because I knew it would bear my not inconsiderable weight. It was a present to myself with my tax refund.
I was active in my 20s, 30s and partway into my 40s, until I married: dancing, playing music and training in aikido. My knees started to give out in my late 40s and I stopped being so physically active.
Right now, I have modest goals -- firstly: to bike to the light rail to get to one of the downtown stations and then bike to work. I'm hoping to be able to bike directly to work by "Bike to Work Day" in late June.