I've cruised the Greek Islands/Turkey quite a few times and it's my pick for the most beautiful and fascinating cruising region on earth. Since you're going in the summer, there will be familes aboard the ship, although most passengers will be older.
But these ports are small walking ports, so you can probably go off on your own and meet people. There are tourists from all over the world vacationing there, and you'll find lots of teens as well.
Hey, my teacher went to the Mediterrean on the Splendour of the seas like last summer. He brought his pictures from it and it looked really cool. Just alot of history and stuff... So if your into the whole history and ruins, and stuff, you will love it. Were going on the Carnival Pride June 2003, and to be honest, i dont think the islands matter. The ship is what i like the most. NEWays, catcha later