My understanding is cardiac deaths early in life are mostly caused by congenital issues that are more likely to shake out under stress, and those late in life are dominated by issues acquired via lifestyle.

Among people under 35 (most athletes) athletes are at significantly higher risk. It's possible tables turn later in life, can't really find a source. Anecdotally I knew two people growing up who died suddenly of congenital heart issues, and both were athletes.