Might you be confusing correlation and causality? Whatever caused your childhood friends to be into intense physical sports, might also be the cause of their ad

Might you be confusing correlation and causality? Whatever caused your childhood friends to be into intense physical sports, might also be the cause of their adulthood health - perhaps a natural inclination to physical activity, or maybe an unusually fast metabolism that gives them lots of energy to burn. Not to suggest that you're wrong - childhood exercise probably is very important, and is under threat.