If you spent your times running marathons in your 20s and 30s, you'd have a good chance of being in for a total hip / knee replacements in your 40s. Swings and roundabouts!
Again anecdotally, I have a keen running doctor friend in the UK who had 2 hip replacements by the time he was 40. Now that he's in his mid 50s, he's looking at replacements for his replacements.
Anecdotally. A friend is a surgeon. Does knees and hips. Says patients are getting younger. E.g. late 30s for total knee replacement is no longer uncommon; usually endurance athletes.
