How do you know you are transgender?
There were about a half dozen boys in the neighborhood and being boys there were always comparisons and competitions. I did not fare very well in either, one that I remember explicitly was 'how big was your wrist?' The measurement was whether you could touch one of your fingers to your thumb when encircling your wrist. I think the oldest couldn't touch any, most could only touch from middle finger to thumb. I could touch them all. As I'm sure you can imagine, that was met with laughter and disdain. In the woods behind my home there is a large evergreen tree growing next to a boulder. The trick was to climb onto the rock then climb the tree. All the neighborhood boys could climb the rock and tree, except me. Eventually I got older and more importantly taller and was able to climb the rock and tree, but the rest of kids had already conquered that obstacle and moved on to other games. During these times I waffled between dreaming of being a girl and hating being the crappy boy that I appeared to be.
You might be thinking "Wait a minute you said 'mostly thought of yourself as a girl most of the time'." Well when I could, I did climb the rock and then I did climb the tree. All the way to the top, it was awesome. Those few "male" successes I had, as limited and delayed that they were, were great. They may have relieved the dysphoria for a moment or two, but it never stopped.