Young guys train really hard, do well, move up to Cat 1. Then they realize that there is a limit to how far they can go in the sport. Time demands are significant. Peers are moving onward and upward with their education and careers. Increasingly it seems career concerns outweigh bike concerns. So they stop racing. Then they hit about 35-40 years old. Time demands are significant, they realize there's also so far they can go in their career. Increasingly, it feels like quality of life is more important than career. Gets back on bike. Gets fitter. Starts racing.