I feel like no one cares?

Im really upset right now, literally in tears. Im turning 13 on Monday, but everyone treats me like a ******* 6 year old. I have a 15 year old brother and a 17 year old sister so Im really used to hanging out with older kids. I have nothing to talk about with girls my age, and I find them incredibly boring and uninteresting. I honestly don't want to spend my time discussing which barbie is the prettiest. I'm on vacation right now with my friend from Europe, Kara. I've known her since birth so were basically best friends. The problem is, is that shes 15 (turning 16) and all of her friendds are 14-19. Of course since Im the youngest I dont run as fast, Im not talkative enough, I cant skate, I dont smoke, I dont have a boyfriend, etc. Kara and I get a long really well but when Im with her and her friends I feel like no one cares about me and all they want to do is find a way to get rid of me. Whenever I'm with Kara and her friend Stacie we have a great time. Stacie actually asks Kara if she can invite me to hang out with them. But when Im with a group of friends (were the only girls there and the rest are guys) no one talks to me. Its not that I feels like Im not there, but it feels like they want to get rid of me. I dont know what the **** to do. I dont like to hang out with kids my age, and older kids dont give a ****.