We sailed on the 1/4 Magic and in our party we had a 19, 20, 21, 17 and 15 year old.
The 17 year old was the only boy. Yes, college age cruisers are onboard, though not as many as the younger ones, obviously. The girls took advantage of all the adult comedy shows, clubs, theme nights, etc. During the day they would lie around the pool and sun or catch a movie. They met a few others in their age group. During the summer months there seemed to be more college age cruisers when we sailed in August and July.
MJ