My BIL had his replaced mid 30's. Never exercised, wasn't fat either. He is back playing golf and stuff but is quite protective about it as he is early diagnosed as there are only 2 or 3 replacements offered as average life is 10 to 15 years.
Cycling is good and I've told him that, but its not stopped him playing three or four days in a row golfing.
They dont have kids though, and he does not do DIY (he is a liability with power tools) so for him it's been great. I have a colleague whose partner had both done and he still climbs mountians....