It's a crap shoot. I got hit by metabolic syndrome -- extreme hypertension and type II diabetes. I exercise, I weigh less and am in better shape than I was 20 years ago, but I'm still on a cardiology professor's frequent-flyer list and gobbling meds by the double-handful. Meanwhile, my wife is a four year cancer survivor (another six months to the all-clear, we hope).

The probability of running into a life-threatening or terminal medical condition approaches unity as we age towards the upper limit of human life expectancy (around 114 years, currently). By the time you hit your forties you probably know people who had an unlucky aggressive early-onset cancer; by the time you hit your fifties you can add heart attacks and strokes to that, and less-well-known problems as well. It's all downhill from here, and unfortunately it's not the kind of ride most people enjoy.