I agree that if your BP is nearly 3' long, he is probably at least 2 years old, not one. What I would call "well-started"which isn't necessarily a bad thing, but it's nice to know the true age of any pet.
BUT, the older he is, the more likely he is to be "set in his ways" so it's even more important to find out exactly what his previous owner (or breeder) fed him, to help assure that he eats well for you & transitions as quickly as possible. The good news is that at his size, he obviously DOES eat, so a week or 2 of refusing food is just a normal settling in time, & nowhere near as consequential as it would be for a new hatchling snake. In fact many new snake owners don't even offer food for at least the first week or two, knowing that the snake will likely refuse to eat anyway, until they feel more "at home".