I went with a group of 10 girls in the same age range and we stayed at the Sheraton on the beach. Not going to recommend that one since it has a small pool and service was lacking.
There are usually some good deals to be had at the Aston resorts. The less expensive resorts usually have a lot of younger people.
Search tripadvisor.com for Aston resorts to see pics. Nothing special but they can be had for cheap.
Sorry-the Aston resorts seem to have been changed to "ResortQuest"
here's their website:
ResortQuest