Well, fitness is relative to age. Biden doesn't drink and doesn't smoke, which help. I don't know how many push ups he claims to be able to do but he does exercise and maintains his weight. I'd say he's statistically far ahead for most in his age group. Anything can happen, but people have mostly focused on questioning his cognition rather than life expectancy. Heck, Jimmy Carter is almost 100 and was active until pretty recently.