RustledTeapot

Typically before you even leave the womb, these days.

And either way, your mother starts treating you differently based on apparent sex.

https://psycnet.apa.org/buy/2005-02259-007

You might not believe in the social construct at birth, but the social construct believes in you. Children are treated differently based on assigned gender from birth.

“Relationships between gender identity and birth sex.”