Depends on how much he money he won. If the amount is not worth it then he can forget about it or he could just continue playing until he aged. I believe he would be mandated to submit KYC when he withdraws the money, if not then I guess he can continue to keep it secret. This is is he isn't that smart.

A kid trying to play on casino would be as resourceful as an adult, I'm sure he could find someone who will just give away his identity for $50.