I've heard that too, and then the female, because she's so young, can end up eggbound. Guess they don't know for sure when they're old enough, so if they're seperate now, I would at least wait till they are "old enough" to breed, incase it does happen unintentionally, at least she'll be old enough to handle it physically. But then again, if they're happy seperate, why change it;)?
:I've heard stories of people's corns breeding at less than a year old, and have tragic endings.
:Not only do you risk potential and un-intentional breeding, but you risk stress and disease as well.
:If they're housed separately now, I don't see why you would want to house them together.