I have cycled around a lot of older folks. I don't see any fallout in the 50's. For men, I don't see a problem until the 70's where balance is a problem. Reaching for a water bottle or riding close to the side of a road becomes an issue for many. I ride behind them so I see that they have trouble keeping a straight line. Speed drops off. Those that cycled at 18-20 now cycle at 16-17. Those that cycled at 16-17 are now at 13-15 mph. For myself, a female at age 59, I have lost the aggression. My speed has slowed from 20 to 17-18 mph. I don't care to work on speed. I ride when I feel like it. Some people have trouble mounting a road bike with bad knees or hips and have to lay the bike down and step into the bike. Mileage has stayed high for most in my club. I've seen a couple of people add risers to the handlebars and switch to straight bar bikes because of back issues, but they keep riding.