I'm of the opinion that given enough time all healthy snakes will eat eventually but BPs can be some of the most stubborn holdouts. I had one go a full year without eating and he was perfectly fine. Since your BP is still young there's nothing wrong with feeding mice. You'll still have plenty of time to transition to rats as your critter becomes more established. I wouldn't force the issue just yet. I would try scenting the rats 3-4 times and if he refuses I'd extend the intervals between feedings each time. After the 1st refusal wait 10 days to offer food again. Wait 2-3 weeks if he refuses a 2nd time, and a full month if he refuses a 3rd time. After 3 refusals give him a very small mouse and start the process again. He'll catch on at some point and once he starts eating rats consistently never offer another mouse. I'm glad I have snakes that will pretty much eat anything/ anytime. Even when a couple of them take winter breaks I don't worry as long as their temps are good and the animal shows no signs of sickness. The hunger always wins.