OP, when, in your mind, would you not allow over nights? Just wondering b/c I could see how this habit could morph into trouble as a child wants to drink or try drugs or sleep with a girl friend, or go to questionable parties. If your child knows that he doesn't have to come home at night or eat dinner with you but once a week, doesn't that provide an awful lot of time where he can do things that you don't know about and you won't know about because you can't check in and observe his behavior or condition?
I know some will say "well, you can't be with him all the time" But, to me, I'm going to minimize the opportunity to the extent I can.
I just don't even understand why boys would want to "sleep over" at a certain age. What is to be gained? How many 16 yr olds are sleeping over with their friends on a regular basis? As a parent, I don't want anyone else's kid to be my parenting responsibility that much either. I'd be saying "go home!"
It may be innocent right now.... but I see trouble brewing when teens have too much time away from accountable eyes. I'd be suspicious of teens who want that much time in someone else's bed/floor/home.