I'm 57
I was riding a Schwinn Varsity 10 speed that I bought used in 1972. Finally bought a Giant ATX760 in 1996, rode it both on the road and trails. In 2003 I got a Bianchi Eros.
I don't take anything special, just a "silver" multi-vitamin, extra E and sellenium. And, of course, red wine.
I haven't slowed down. I'm actually in better shape than a few years ago.
I ride for fitness and fun. Now that I am retired (64 days!) I am riding more. In fact, people I don't even know are stopping me to say they saw me 'way out of town on some hill. I average 130-150 miles a week, riding about 5 days a week. Nothing under 15 miles at a time and I try to get in a couple 50 - 70 milers a month. I've done a few centuries, too. I've put 5000 miles on my road bike in 30 months. I live in snow country, so can't ride much from October to March.
Riding is my primary exercise. I walk with my wife now and then, a little golf. I climbed 62 stairs several times a day for 33 years and 12 days when I was working.