I ran into this problem when I tried to rent out a house in Myrtle Beach; apparently in order to do so, you have to be over 25. Luckily though there's these graduation sites that let you rent out houses there, but in Cherry Grove, which is like right next to Myrtle Beach. So that's what I did.
Check out the house;
http://www.myrtlebeachgraduation.com/sand_club.htm
If you drive yourself down there, between July 22nd-29th free to sleep on the floor