When I look back on my childhood I can definitely see signs early on but I don't think that I thought of myself as literally being a boy. I think I was happy being a girl because my parent's basically let me do and wear what I wanted, so I didn't really have a lot of girly toys or clothes anyway. I spent most of my time reading books, building with lego, riding bikes, splashing in puddles and climbing trees. I put together a photo slideshow for my 21st and got told afterwards that some of the pictures that mum had sent me to put in it were actually of my older brother. Apparently neither of us could tell the difference. I also still have a scar on my bottom lip from when I decided to try shaving my face at the age of 7 or 8, so I guess there must have been something going on even then. Despite all this though I just can't remember whether I thought I was a boy or a girl, I guess maybe I just didn't think about it.
Although I often acted more male as a kid, I think that when I went through puberty was the first time I really felt uncomfortable with being female.
I also find it really interesting how many people have said that being interested in guys delayed them realising that they were one. The same thing happened to me, I knew I was primarily interested dudes, and the best way to get guys to date you is obviously not to be one, so being acting girly made more sense.