There's no one answer for this question as each person is different. What I would like to point out is that extreme exercise can put a lot of stress on the body. Soreness and micro tears on muscles increase inflammation and cortisol, so intense exercise can leave the body in a state of stress...more stress ignites if you don't refuel and repair it properly.
In addition to diet and exercise, there may be other things that contribute to an early death. Genetics, environmental factors, poor digestion, poor sleep, etc. are just a few. It's the same with cancer. I've known people who eat right, exercise and lead a healthy life, but unfortunately are diagnosed with cancer.
It is up to us to do everything in our power to reduce the chances of getting ill, but some things are out of our control.
Here's a recent study about running: