I remember something from the Psychology courses I took in University ...20-some years ago. It was commenting on the natural progression of the human psyche, and how the teenage years were so integral to that. That the teenage years are the first time that the 'child' breaks away from the 'family' and starts to form its own identity. The first time we as parents need to learn not to 'tell' but to give our kids options. They don't necessarily both have to be GOOD options, though. (You can get in the boat and calm down. OR you can swim all the way home.
Hmmm...and I got distracted in my head. K, how this is relevant to the current topic is that you may want to bring poly/mono up as OPTIONS to your teenager. Neither one is bad. Both have a long and happy history. Yes, this is something we kept from you when you were younger. BECAUSE you were too young before. NOW we hope you are mature enough to understand.
Just a thought?