Re: "...it happens a lot earier than college"
I realize this is n=1, but my wife, whose father is a chemist, decided to go into social psychology. She took chemistry and hard maths in high school and university. She never once heard a teacher or professor say women shouldn't go into science, directed at her or at any other girl in the classroom. Nonetheless, she was only one of three girls in advanced girls in high school advanced chemistry.
Well, considering my wife's observations, perhaps we can day it's n>1.