I have a forum like this. I am about a year older than you, but I think that when I was thirteen, I was that big. But, I don't have underarm hair. However my moustache is starting to come in, as in I can see white hairs on my upper lip when I look close in the mirror and I can feel them with my bottom lip. How much pubic hair do you have? Mine is short and wiry, a couple are about an inch long. I don't have very much at all, and it can be seen when I stand a foot away from the mirror.
Well, I guess we all develop differently. That's what sucks about puberty; it's almost impossible to find someone who's both at the stage you're at with almost everything like yours, AND you can talk to them comfortably about it.