https://theconversation.com/gender-conformity-starts-young-and-boys-and-girls-fall-in-line-in-different-ways-275996
"It’s also unclear to us why girls’ responses to perceived threats to gender conformity may weaken with age"
that's because "male" is the top of the social hierarchy. a person, perceived as female, displays male tendencies that is still a net positive (moving up the social hierarchy). conversely, males displaying feminine tendencies are purposefully degrading their social standing and that is, to them, insane (moving down the social hierarchy).
I came to the same conclusion in high school. I spent my entire childhood trying to fit in and nothing I did worked so I gave up trying. a huge part of that was being autistic, which I didn't figure out I had until my 40's. the best part is being 55 I have completely lost all fucks to give about how i'm perceived by others.