Have been a long time reader of Overcoming Bias, but haven't gone over to LW after the split.
I've been a rationalist as far back as I can remember, but I really became serious when I was 12. I grew up in Israel, and I was being prepared for my Bar Mitzvah by a Hasidic Rabbi. As Hasidim are prone to do he was telling me some mystical story, wherein he mentioned that the Sun orbits the Earth. I correct him offhand that this must be wrong. He countered with what I now know to be a classic "Have you ever been to space yourself?" followed by the even more classic "Maimonides said so, you're not saying you know better than the Rambam, are you?". I knew so clearly he was wrong, I could explain roughly how it wouldn't really make sense given what we know about gravity, etc., but I couldn't really even convince myself how one might reach that conclusion from scratch. As a 12 year old I vowed to never be in such a position again. (Although my Bar Mitzvah went off flawlessly, I'm now an avowed non-theist in the presence of religious folks, atheist otherwise)
My academic training was in Linguistics and Computer Science, and I'm currently working on a startup in Silicon Valley.