Just to add to the thread.

I ride a lot with one guy in his mid 60s and the other will be 75 in March. Both are very good and can pull around 20Mph average on a 100 mile ride. There are also a lot of other riders in our area in their 60s, 70s and 80s who ride anywhere from 50-125 miles a week.

I'm the young-un at 59 but I just started at age 57