I used to be a regular runner until my early 50s when a knee injury made me stop. I know, because of timed runs over the years, that my speed dropped a lot in my 30s, 40s and 50s despite me putting the same effort in - but I still enjoyed running as much.

There is no doubt that performance reduces with age, including cycling performance, unless an older rider was just not any good in their younger years and has taken it more seriously later in life.

I'm not saying one cannot perform well in old age but IMO a good (or reasonably good) youngster will always beat a good old timer.