Why is most of my generation(13-18) so immature?

Most of my generation are so effin immature and a word I can't use. Some in my generation are so immature that if observed by an adult, the adult would think that they're not straight. And it's not just the immature thing that bothers me (I like laughing at them), but it's when they act a like a (the body part that you sit on) almost all the time. They talk about other people negatively behind their backs(even their "friends"). And I think the meaning of "friend" lost meaning in our generation. I'm in the IB program so I expected mostly nice, weird nerds, but no it's concentrated with (synonym for behind). Wth? What went wrong? Are parents teaching children something wrong? Has been there a birth defect in our generation? Or is it just the "American" attitude? I'm American, so take no offense at this.