Greetings, Anna! I am happy to hear from you! And i want to advice you something what i do know about that.
To my mind, people become vegetarians because of couple reasons - because it's fanshionable right now and because they do not want to hurt the animals. But, all over the world there are lots of examples, that vegetarians can keep fit. They do some drinks with protein or just find it in eggs or breeds.
But i think teens should not do it because we are growing up and we should get every kind of vitamins.
I hope, my advices will help me.
Take care of yourself