Christian, why not sort of find a middle of the road place. You want your snake over to rats but are worried a weaned rat, which does have erupted teeth, might be too much for the snake since he's never had rats before. How about instead you see if you can get a few fuzzy or very young pup rats and see how he goes on a few of them first. If he's doing well and hitting on rats strongly you could move slowly up to the size you want to feed him.