I remember it happening in the sixties, but it started (at least in my area) a little earlier than that. When my parents were growing up a girl would not dream of wearing pants or slacks out in public. Jeans might be worn if she were working in the field in slopping hogs.
I found a letter my mother wrote to my grandmother in the early sixties, when I was a baby. She referred to a woman she just met who wore pants and smoked and it was considered so gross and unusual.
I also recall in the seventies in school girls could not wear pants unless it was under freezing—and the weather was checked every morning and girls who tried to get away with dressing like boys were sent home. And female teachers were never allowed to wear pants or slacks.
That’s where it all started—that’s what brought us to where we are today, boys wearing dresses to the prom.
Girls didn’t wear pants in the 50s even when they came out to observe street racing, they wore dresses.
Pants weren’t even allowed by girls in school under any condition.
I can’t speak for the 60s since I was too busy running a business to give a damn.
From your post i’m old enough to be your father since I was married in the 50s.
And what have we for it? Nothing of value. Isn’t it strange to realize that are one time people were really disgusted by gross things and didn’t apologize for the natural reactions?