My guess is that most of those houses where you see many college kids are not intentionally rented to college kids. I may be wrong, but just based on our experience and everyone we know who is in the rental market, none of them would knowingly rent to a house of under 25 for all of the obvious reasons. All have it in their contracts. If what Beach Runner said on another thread about parents renting the houses for these spawn of theirs to use is true, then the parents are lying for the kids. Small wonder then about the kids behavior.
This is a fear of mine, getting guests that have lied on their contract to us and break rules. My wife does an excellent job of screening (we *think*), and based on what our house keeper tells us, usually they respect the house, the beach, etc. But it could happen.
If these places are knowingly being rented to a group of under 25, then the parties doing the rental are idiots. Do you know if the particular houses you referred to are owner-rented or via a management company?