Firstly, Welcome to the Boards!
There are lots of teens on here that write YA, MG, and everything else. Sure, there are people who will say that you can't write it because you're a teen, but you can't let other people tell you what you can and can't do. That's completely up to you.
If you feel that you can't write about teen issues, then you shouldn't. You should write what you feel comfortable with. But you should also ask yourself
why you don't think you can write about said issues. Actually, looking back at your post, maybe you mean that you don't want to write about the stuff because people will assume that you have the issues...
If that's the case, forget them. People will always assume that a writer is writing about themself. It's rarely true (in my opinion). You can write about whatever you want. I've written about the use of cocaine, heroine, and lsd when I've never done anything like that. I've written about two girls that fall in love when I'm a guy and obviously can't do that. I've written about characters with depression, eating disorders, family problems, and tons of other things. I don't personally experience all of this, but I write it because I want to. You should write whatever you want because that's what you want to do.
And who cares what your peers think? You'll be the one laughing at them when you make a name for yourself doing something you love to do while they word some dead-end job they hate.
You can definitely use a pseudonym, if you want to. A lot of writers do it. I'm considering it. But don't think about it too much. Just focus on your writing.
If you feel more comfortable starting off with a safer MG topic, by all means write it. But don't forget that you want to push yourself, since that's the only way you can get better in the long run.
And one last thing...don't worry too much about what people will think if you're a teen writing for teens. As you'll find out when you look around here some more, it can take years to land and agent and then just as long to get an editor. It's quite possible that you won't be a teen anymore when your book hits the market. I'm not saying this is true for everyone. There definitely have been published writers under 18. But don't get ahead of yourself...
Good luck! and keep your head up