It's not just "top level" athletes. I know a number of people with stuffed knees, lower backs, hips and, yes, more knees. And they are one and all under 30. Many were injured during their school years, some after. So you don't have to be a powerlifter/bodybuilder/strongman/etc to have stuffed shoulders, knees or other joints.
Considering what the top 5% go through to get where they are, they are not doing too badly, compared to the general population. Besides, I think that you have a fair whack of old women having hip replacements, mostly from genetically induced arthritis but also from obesity. You can't carry around the equivalent of 3 plates of excess fat without it wearing something out.
If you want to be the best, you have to push your limits. But the best of the best know when to back off to enjoy longevity in their sport.