I know someone (a little) who is a grandmaster. He obtained the title maybe around age 17 (+/- 2y) after doing it basically full-time through his youth, with strong family support, after showing strong promise at age 3. I'm pretty sure he and his family are glad of it, and it was a lot of work. His brothers and father are also very good at chess and have taught (rated, but not IMs I think).

I'm very glad (AFAIK) he didn't have to abuse his body etc to get to that point. That doesn't seem worth it.