I am 62 and have been riding well over 30 years and being retired now I average 100 to 140 miles a week depending on how I really fee.l some rides are great otherr rides aren't. I try to listen to my body and what it is telling me which usually works, however lately I can do the miles , but I just don't have the speed like I use too. Could be over training which is what I believe it is or due to age and other factors I am starting to slow down. I really can't put my finger on it but as long as I am riding or doing some form of a workout it is all good imho.