I'm 15 (almost 16) and all of my cruises except 2 or 3 have gone to Alaska. I love Alaska because it's so beautiful! The number of teens depends on what time of the year you're going at. So if it's summer or any breaks then there will probably be teens. When my mom and I go, it depends on the price so we just book if it's cheaper which is usually not in the summer time lol. But all the times I went, there were usually a few kids there... can't gurantee if there will be for you but just enjoy the scenery and food!!
oh btw, I'm going to alaska on the serenade of the seas on may 16th!