I read in an article published after Worlds (in japanese) that he's had asthma since he was 3 years old and that he takes medication for it twice a day. Unfortunately I can't find it anymore, but perhaps wxunxx can? (thank you for joining, by the way, I've been reading you... I was hoping you'd start writing here too, I'm glad you did)
I'm sorry because I'm probably stating the obvious, but I'm pretty sure that being 18 years old (and a half) qualifies someone as a young adult, not a kid. As in, someone who's almost, if not completely finished growing physically, someone who can get married and start a family, who can vote etc.
Besides that, I won't comment on his health, because I can only take what he says for granted, can't I? I'm a student of foreign languages, not medicine; I'm not his mother, nor his sister, nor his coach. The closest I've ever been to him in my whole life, physically, was when he competed at the JGP in Merano, but I didn't even know he existed I don't see him train every day, I don't know what he does besides those few minutes I see him compete or train in tv clips. As such, I can't pretend to know more than he does, or the people that are around him do. How could I? As a fan, I can only hope he takes care of himself, but if he doesn't, well, it's his life, his career, his choices. He's old enough, I'd say.