This is a really interesting thread, so many topic changes... but the most recent one:
I don't think there is any such thing as "too young". Whatever you feel right now is completely valid. As long as you accept that there is no definite "end point" - no place at which you can go, "right, never going to change anymore!" I'm twenty and I'm very confident in my identity at the moment, but at the same time I don't know if I'll always feel the way I feel now, or always think of myself as the same person. Whatever I feel now is true for now, and as far as I'm concerned it will be true for the foreseeable future. But if I ever stop changing it'll be because I'm dead.
So, no, 13 isn't too young! If it's how you feel then it's true, and if you want to tell people then you should. Coming out can be really empowering, and it can also be a huge relief. But sometimes it can also be really hard, and in some ways it might be good to get it over and done with sooner rather than later. My parents were reasonably good about it when I came out (apart from a couple of weird things, but that's another story) but they're certainly much better now, six or seven years later. I'm glad I told them when I did, it's made life since then so much more pleasant. They may not have liked every girlfriend I've ever had, but the point is they've known about all of them. And that's been really important for me.
Go you! Whatever you want to do there's no "right age". Don't let other people's reactions put you off to much, this is about you, not about them.
I just re-read my post: I'm so opinionated! This is just what I believe...