It's funny to me how many of us realized our non-belief by the act of reading the bible. Just like you, I read the book when I was a 13-14 years old.
Unlike you I hadn't had years of indoctrination spurring me to do so. I'd been given very little religion, I was told what my mom believed and expected to believe it too. I read the Bible, not to answer questions, but to cement my faith with knowledge. It had the direct opposite effect. I was so thoroughly horrified that I rejected the lot of it.