It looks like a RTB to me easily. The tail is more brown though.. I'm not sure if that is a trait more common with wild boas.

Considering you mentioned that he has grown I would assume he's eating well, yes? Does he show any sign of breathing issues, weird poop, ext.

It could be a good idea to get him to the vet for a check-up, but if he seems pretty healthy than thats completely up to you.

How big is he? Weight or length would be fine.