Hi Susan
The key thing to say here is that we aren’t publishers. We are literary agents.  So we are the ones that represent authors – not the ones who get the books on to the shelves. 
We are certainly open to representing teenagers, but representation is a highly selective process and we receive many submissions. We are happy to see your submission, if you follow our guidelines on this site, but the more you keep reading widely and developing your writing, the more likely you are to achieve your goal. 
Good luck!
Sarah