Hello Less Wrong!
I'm 16, female, and a senior in high school. Before I started reading here, I was not particularly interested in math, science, or rationality (which I had never really heard of). I stumbled on Harry Potter and the Methods of Rationality in October, and fell in love immediately. I read through the whole story in one night, and finally made the leap to Less Wrong during Eliezer's hiatus.
I started on Less Wrong by reading Mysterious Answers to Mysterious Questions and within three posts I realized that, for the first time in my life, I was surrounded by people significantly smarter than me. Some people would probably have been excited about that; I was terrified. I promised myself that I wouldn't post - wouldn't even create an account, to avoid the temptation of posting - until I had read all the sequences and understood everything everyone said.
In retrospect, that may have been setting the bar a little too high for myself, especially since seven more sequences were added while I was reading. I eventually revised my standard to "I will not comment until I'm sure I actually have something to add to a discussion, and until I understand the things I have read well enough to explain them convincingly to 4 of my friends."
The fact that I had to set all of those hurdles for myself just to have the self-confidence to create an account probably tells you a little about myself - I'm not ordinarily insecure, but I was so excited to find something like this I was very worried about "messing it up". I've now read about 90% of the sequences and 98% of everything posted on Less Wrong in the last few months, and understood almost all of it (the quantum physics and decision theory sequences still confuse me). I'm not sure "read everything before you start to contribute" is generally a good guideline for new visitors, but for me it was perfect. I changed my mind about a lot of important things along the way - if there's enough interest, I may discuss this in a post about exposing more teenagers to rationality.
So, thank you all for this great site! I hope I'll be able to contribute.
Welcome. Just remember: don't take the posts on LessWrong as gospel, so to speak, just because of their source. Eliezer has posted about this several times, though, so you most probably need no reminding.