I once read an article suggesting that tennis legend Bjorn Borg was an extraordinary athlete even compared to others at the top of their professions. His resting heart rate was once measured at less than 40 beats per minute, which was a big reason why he was able to perform at his peak even in long, grueling matches.
I don’t think life expectancy and health risks have any bearing on whether someone is an athlete or not, I just don’t think there are objective measures. Someone who does nothing more than watching his diet and living everyday life may life a healthy life to the age of 99, but they can’t be called an athlete.
If an athlete must engage in a sport, then it boils down to what the definition of a sport is.
We can all agree that at one end of the spectrum (from a purely physical point of view) taking a nap in a comfortable hammock isn’t a sport. At the other end of the spectrum might be a marathon run. What lies in between?
I played hockey for a long time, and that seemed like a sport to me, even though as a goalie, I didn’t have to skate the same way everyone else did. I played basketball and that seemed like a sport, football as well. Wrestling, definitely.
Is skydiving a sport? How about scuba diving? Or mountain climbing? That is pretty specialized, and doing it can’t be healthy or lifespan extending, especially if you are climbing Everest.
And let's not overlook the dangers of high level chess!
It'll positively mess with yer mind!!