@kamishiniyari Ballet messes up your feet if you do it right, and it fucks them up severely if you do it wrong, in addition to your knees and tendons and such. It also involves extreme physical exertion, and you need to temper your body a lot to pull it off at a pro level. The motions are meant to be so smooth and precise that even the tiniest dip in performance becomes visible, especially to professional judges.
Humans are already past their peak at 30, so it becomes impossible to keep up with the extreme demands it has on your body when you're 35 at the very latest. At that point, you're left with skills you've been practicing since 8 and can't use anymore, with few other skills because of how much you needed to practice for ballet. And it's not like you've earned enough for a lifetime because ballet isn't that popular and prestigious. The best you can do then is to become a poorly-paid ballet teacher or abandon everything you've worked for so far and do something entirely different.
It's not quite as bad as a crack habit in terms of how much it'll fuck your life up, but it's up there.