Any writer of YA fiction knows that one of the things - if not the thing - editors look for in a manuscript is an authentic voice. Voice encompasses the whole of the book, it gives a reader a 'feel' for the characters and story. A writer's voice infuses the entire story and one of the ways to demonstrate that voice is through dialogue. However, when your main character is a teen many writers feel that they need to write the dialogue in a certain way - like there's a 'typical' teen voice or something. Well, we all know that there's no such thing as typical. There are stereotypes for sure but no writer wants their character to be a stereotype. Yet I've noticed some writers who want to write YA seem to fixate on the dialogue and mannerisms of teens by asking themselves or other writers whether they think a teen would say this or do that. My response to the question? "I don't know about whether a teen would say this or do that but what would your character say or do?"
I write fiction that, for the most part, has older teens as the main characters. But it's not like there's a template that says what all 17-year-old girl protagonists sound like. I have the privilege (or is it the curse?? :) ) of being a parent to two teen girls. Those two girls sound, look and act nothing alike. Their friends sound, look and act differently as well. They are all individuals. Some of them sound extremely mature and adult, others more child-like and innocent. One 16 year-old-girl could say "Like, I totally can't deal with her drama." while another would say "Drama queen. She better grow up." while another would say "Well, she seem kind of emotional. Don't you think?" They're all conveying the same point about another character but saying it in different ways depending on their maturity level, personality type and style. The voice comes from the character. Always.
What really bugs me is how fixed so many people seem to be on making sure that voice 'sounds' teen enough. Maybe it's because I'm embedded in the YA world but I don’t hear nearly as much chatter about whether your sixty-five-year-old grandmother character sounds 'senior' enough. Yes, we as writers have to make sure that we don't make a teen sound like she's a neurosurgeon when she's only taking basic Biology in high school (unless she's some kind of super-genius or something. But then why would she be taking basic biology then? I digress.) but your manuscript is filled with a variety of characters with a variety of ages and backgrounds and you have to create several unique, realistic voices.
So the point of my semi-rant? Worry about the character and making the dialogue true to that character. Don't write what you think a teen should sound like. There is no typical teen voice. There is only emotional honesty. Once you nail that, everything else is gravy.