Like another commenter, I was in my 20s. I had no background in Math or CS when I read GEB. I was just a self taught C programmer writing door games for BBS systems. I read it cover to cover and it inflated my mind like a segmented bouncy castle. I had whole rooms to play in that I had never even realized were in there. Parts of it were slow, but I just put that down to my ignorance and plowed on. I can honestly say the book changed my life.