Regarding the sudden death thing that seems to affect some high profile athletes who stayed in good shape after retirement, that would be among the least of my worries. If it happens, I probably won't even know it, or it'll be over with quickly even if I'm aware of it.
Among the most recent I can recall offhand was Marvelous Marvin Hagler, the retired middleweight boxing champion who died unexpectedly earlier this year at 66. Not "young," but Hagler was always well disciplined, stayed in good shape after retirement, and wasn't known to abuse drugs or booze (other than a brief period after his final career loss to Ray Leonard, according to insiders who knew Hagler back in the late 1980s-early '90s). He was often interviewed later in life and always seemed mentally sharp, and looked fit.
And the odds are that most folks who stay fit, eat well, get enough rest, etc., will live long enough to die of some lingering misery anyway. Considering how my parents and grandparents went out -- all lingering deaths, after years with cancer, COPD, congestive heart failure and/or dementia -- I'd rather go for the quick unexpected finish, preferably during a bike ride or run, or maybe while sleeping.