I'm 67. A 17 mile ride, even every day would just be a warm up. I quit riding when I was 57 because my knees were shot. 8 years later, almost a year after having both knees replaced, I took up riding again. After two years back, I'm riding regular 50 mile mountain routes that are harder than I did from age 50-57. I always rode ever other day, to have time for recovery. My average speed is about 2 mph slower than 10 years ago, so my 50 mile rides take longer than they used to, but the lower speed doesn't detract from my enjoyment of the rides. I regularly ride scenic routes from Loveland to Estes Park and around several local lakes. During the tourist season, I ride avoid weekend rides due to too much traffic. I have some 10-12% grades on my routes, so low gearing is a must.