I never bothered checking the reference, but a long time ago my cycling coach said something about a study in which they had discovered that a majority of former elite and pro cyclists had dropped out of cycling after stopping racing.

I see lots of older cyclists, but rarely are they former racers. Maybe those who start early and go really hard are less likely to get out there in their 50s, leaving a chance to all of us who are late-bloomers athletically speaking.