For what it's worth, Sonnon started out with a genetic disorder that affects his connective tissue. This means he's a lot more careful about recovery than anyone else I've heard of.

That exercise works to some extent is clear... However i do not see a lot of evidence based work on exercises that find a good balance between health and body damage.

Are you talking about a specific type of high-performance exercise, or exercise in general? If the former, maybe you're right, but I still kinda doubt it. If the latter...yeah, maybe a 40-year-old bodybuilder doesn't look or feel as healthy as a 20-year-old bodybuilder. But I would bet you a lot of money that they are healthier than a 40-year-old who spent those 20 years not exercising.

In general, I think, the direct health benefits of exercise (lower risk of heart disease, lower risk of osteoporosis) happen even with half an hour a day of fairly gentle aerobic exercise. Beyond that, you get what you train for. By that I mean: if you want to be able to run a marathon, you have to practice running long distances fast. If you want to be able to lift 400 pounds, you have to practice lifting heavy weights. The human body adapts to the load expected of it; that's the whole point of exercise.

There are always tradeoffs, of course. Lifting weights is hard on your joints. Running can be too. But I've known plenty of people who are in their 40s, are very fit, and have managed to avoid injuries. (Granted, they were people who had done swimming, cross-country skiing, martial arts, that kind of thing. Not bodybuilding, which might be a bit more 'unbalanced.' Older people do have to be careful to avoid injuries and do take longer to recover than younger people.)