That's pretty borderline in my opinion. When I was 14 I went out with a 13 year old. It was a school event so it had chaperones. Even though I went out with a 13 year old myself , looking at it now, that is awfully young. You are a year older than I was, and at your age an extra year makes a really big difference.
Does her parents know? If both of your parents know and are OK with it, then I'd say give it a try and see how it goes. And keep it innocent. If you want to sneak behind your parent's back, then I'd say you aren't ready to be dating.
I don't see why not... it's only two years. However, as some other people have said, she is still in middle school. AKA you might find that she's a little more immature than yourself. And if you date her and then break up, you'll have a bunch of random 12 year olds blowing up your phone bitching you out for breaking her heart... js.