I guess it all started around age 10 for me.. I was exploring my sexuality a bit, which was confusing. And interactions with others became complex.. It was difficult for me to adapt to male gender roles and to deal with other kids while they were developing too. I just felt like I was on the wrong side of things. Felt like it'd be so much easier being female, because it's more 'me'. Like I wouldn't have to deal with guy BS and trying to measure up to all my guy friends. At one point I ran home after some confrontation with some people and nearly killed myself. For a while I just cried myself to sleep wishing I'd wake up as a girl. So for me, it was a lot of mental stuff, especially dealing with gender roles and gender-based interactions with others.
The physical changes weren't too sudden or major, and I guess I expected it all to happen. But the weird thing is, at one point I forgot I wanted to be a girl. I guess it was all too traumatic to deal with, so I suddenly started focusing on being more of a guy and being 'acceptable'. It softened the blow of puberty I suppose. So between 12-13 and maybe 15 I was trying to improve myself and become 'cooler' and more masculine, instead of the pathetic lil freak that I used to be. It worked, especially smoking pot with people. I had some good friends too, so it wasn't so bad. Fell into a certain persona that worked for me. Nothing tooo masculine, but was 'acceptable'. And that's how I survived puberty and my teens... just repressed the dysphoria away.. :/