how many 17 year olds are hanging around much older men because they need a buddy and 17 year olds don't often hang around their own dads much less step-dads or step-boyfriends, they're out with girlfriends or hanging around their peers. I'm not sure, but I know there are a lot of teenagers now who don't have a father-figure in their lives at all. None, nada, zip. Some of them do crave a masculine role model.
Of course those kind are more easily victimized by chicken hawks. Mohammed had kids of his own, it's a little strange he would go to such lengths to "adopt" a kid when he wasn't seeing his own.