Rosy boas are not the smartest snakes I've kept, but they are among the most food-directed; in combination, dumb and hungry equals bitey.
No, they don't grow out of it -- I've noticed that if anything it gets worse, especially in breeding age females. I have thirteen rosies currently, and seven will bite every time (all my
orcutti but one), and a couple of the others will if I don't pay attention.
I never handle rodents before handling any snakes that may bite. It is a simple order-of-operations routine to do snake care first, rodent care last.