I agree, physical bodies aside, the outward presentation of gender is a social construct. Boys could (can and do) wear pink and they're still boys. Girls are still girls even if they play sports or do other typically "masculine" activites.
As far as my own understanding, it wasn't so much a choice to be a female as it was to not pretend to be a male anymore. I got depressed watching children play on the beach, who does that? And when I fully understood it, it was depressing to watch children just be children without that "noise" (I compare it to a radio broadcasting static, rather loudly) in their head that we (non-cisgendered) experience at some point or another. Had I grown up with a female body, I would have avoided all the chaos that went with being a transgendered child in the (early) 1980s. Again, it wasn't about being male or female, it was about not having to fight mental chaos.
I don't like my male body. I do like the parts of me that are female(ish), my breasts, etc. If that was male, I'd like being male, but it's not and I don't.