I have had experience cruising as a minor.
My first cruise (SS Universe Explorer), I was about 14yo on an educational cruise in Alaska, most passenger were retired school teachers and educators. I had a blast with everybody, including my grandparents that took me. The conversation was amazing, as was the food and the numerous lectures.
The second cruise I went on I was 19 and in college, I'm not the stereotypical crazy college student (I took my grandmother with me). Carnival's Miracle was a lot of fun, tons of excursion options and the demographics of the passengers seemed very broad. I had a BLAST on both cruises. my grandmother shocked me with all the excursion she was willing to try with me.
In my opinion, every cruise is what you make it. Go with an open mind, enough money to do what you want and HAVE FUN!