My cousin is 14, born a female and now "out" as a ftm transgender. It's honestly a sad story. She knows I'm conservative but we talked about it for a while and why she wants to be a boy.
She said puberty was uncomfortable and she hated getting her period. She's always been athletic so she didn't like that boys got stronger and better at sports than her as she got older. "It feels like no matter how hard I try as a girl I'll never be as good so nothing is worth it." - her words. She said she thought girly stuff was stupid and never really liked it, and that she was afraid of being sexualized as she got older. She said she thinks she's trans because all her friends are boys and she never liked wearing dresses and stuff.
Interestingly enough, she's actually kind of conservative for her age on a lot of issues. She's made fun of Biden before and likes hunting and fishing and stuff. She likes Trump.
Just thought I'd offer a first person account I guess. It's a sad story.
I think this is why they are so desperate to get kids on puberty blockers as young as possible, so the sex hormones never fully kick in and thus they never realize they were never trans.