Usually teens start writing poetry (usually girls) around the age of 13-15. They discover poetry can be an outlet for those inner most emotions of pain they attain from parents, boyfriends, and social conflicts in their lives. It usually starts with fixed rhyme emotional speeches to the person they hate, then it moves to free verse poetry about anything and everything they feel a horrible dread, or "angst" about.
It's not bad. It's good for teens to have an outlet or coping device for their depressions and anxieties. The problem comes in that they write so much and want to share it. They usually have quite an ego about their ability to reflect their "powerful" emotions through their writings. Any recommendations for improvements are taken with emotion and usually they are very very reluctant to read classic poetry or the poetry of other amateurs.
Teen angst poetry is not publication quality. It is a horribly common venting tool. If you want publication, you have to stand out from the depressed sulking majority. That's not to say anything with a depressed theme is bad. See the characteristics to compare with your own work.