I will be 82 this year. I have always just rode for fun and exercise, and still do. Depending on what usual route I ride, I ride from 20 to 35 miles every other day. I find that a recovery day off works well for me. I have been blessed with unusually good health all my life. I could easily pass for someone 15 years younger, and that is backed up by my doctor. About the only thing I have noticed about old age is the fact I dont have the stamina I used to. How ever I have given up almost nothing, it just takes a little longer. I for instance still do my own oil changes and tire rotations, plus other external maintence on my car. As I have posted before, if you set you rust.
There is an internet site I belong to---------------------- The Royal Academy of Octogenarian Cyclist. It is a sub group of Facebook.