Mine are seven months old and seem to have settled. They've only been nippy when prospective buyers sex them, which I guess is understandable.

I would leave him alone for a week, make sure he has appropriate temps/humidity/hide, feed him, then handle him for a few minutes each day starting 2 days after you feed. BRB's, like other boas, shouldn't be on a heavy diet. A feeder that leaves a barely noticeable lump weekly is fine.

One trick that helped cure mine of nipping was I would make a fist, put my hand in the tub, and let them hit the back of my hand a few times until they gave up; they learned that biting did not make me go away. Same when you handle them, don't put them away right after they nip, only after they've been chill for a bit, so you don't teach them that biting = go home.