My DD chose to celebrate her 13th birthday on the Magic, so was the youngest teen in the group. For some things, the teens are divided into 13-15 and 16-17. There is "hanging out," but there is a long list of activities that can be done at any time (just ask CM for supplies), as well as some scheduled stuff.
We do travel "off season." so there are not tons of teens on board. We had only one small problem and the counsellors took care of that as soon as they were made aware of if (a young man was behaving inappropriately toward my daughter).
DD had a blast. Of course, she views the Magic as her second home....
Just for your info, there are security personnel assigned specifically to the teens. There is an information session on the first night which includes a security briefing. DD reported that when she and a friend were walking on deck 9 at night they were "followed" by an officer. She asked whether he was following them, and he replied that he was doing his job. She laughed and said that his job was to watch them! Be aware..they were not doing anything wrong. THey just asked if they could stay up late and see what went on around the ship when everyone was sleeping.
Yes, there are some horror stories of things teens tried to get away with...but you have to know and trust your kids. Fortunately, mine seems to tell me everything. She is quite convinced that she can arrange anything on the ship--as in "what is that special food you liked in Palo? I know the head of Palo and I can see if he will get it for you ...." She prides herself on arranging for our favorite server, etc. She was heartbroken when Jacqui transferred to the Wonder.