Well I stopped at about 51 just to devote proper time to my mid-life crises and to tell the truth thought the hammering my behind was getting was slowing me down that way.....I refused to believe I was getting old
After 11 years off I gained a bit of a belly and decided to come back with a different seat. It could be a number of reasons someone quits riding but it doesn't sound like too much fun at other things is your friend's problem. My best friend was the athlete when we were kids and now he's totally fat with all kinds of surgery and problems and retiring early. I feel for him alright but.....Things like that motivate me to stay active.