There appear to be two main hurdles in establishing a level of performance in endurance sports. The first is setting and maintaining a routine. This is often done in the company of others (the Wednesday morning group ride, the weekend club race etc). The second is getting back up after injury. This is often a solo ordeal.
The older cyclist doesn’t bounce well. More specifically, they don’t bounce back well. There are many reasons for this but at least two come to mind. The first is intrinsic. Older people simply do not have the same depth of physical reserve to take up any slack when one system takes a hit. Running with an injured knee can throw out the hip. Getting back in the saddle after missing a couple of weeks of riding taxes an already stretched cardiovascular system.
The second reason is extrinsic. In my age bracket (30-50 years old) work and family commitments form a large part of the daily routine. Sports like bicycle riding play a secondary role and have to fit around these core activities. If the recovering ride (run, paddle, etc) requires a further period of recovery on the sofa watching videos (or in front of the computer posting a blog) and violates these responsibilities then the ramifications can be profound. More often it is the anticipation of such outcomes that dampens the enthusiasm to return to the sport.
These are excuses. Let’s not forget the majestic words of Ronnie Johns