I'd bet most or all of the people who'd let their young sons wear princess dresses to teach them that gender specific clothes don't matter have put pink dresses on their baby girls and blue onsies on their sons. That means the parents were actually teaching babies gender appropriate clothes from babyhood.
How many of you decorated your son's nursery with tinkerbell, Cinderella or other girly things? I'd bet none. So you started early creating the distinctions with boy things for boys and girl things for girls.
Unless you raise you child gender neutral from birth, which I doubt many do.
Um... my baby girl slept in my bed with me until she was big enough to move onto a mattress in her own room. I didn't "decorate" at all.
She wore hand-me-downs in any colour, including the cutest little jean jacket, which I painted with dragons. She wore whatever I found at the Sally Ann that appealed to me, or arrived on my doorstep in giant bags from the neighbours.
My baby SON also slept in my bed with me, until we realized he couldn't sleep like that, then he moved into a folding travel crib in his sister's room. Eventually he graduated to a single bed that he shared with his sister.
HE wore his sister's hand-me-downs until he was... well, basically until he got to be the same size as his sister. I mean, honestly, who cares if a 2yo boy's blue jeans have flowers on them? Certainly my boy didn't, and neither did anyone else.
I didn't set out to raise them "Gender neutral", and actually I'm pretty sure I didn't. I was just being practical. By about three they were choosing their own clothes.
That said, I was very pleased when my son was six and won a giant pink and blue pastel bunny in a church raffle. The folks at the church hesitated to give it to him, because they were worried that he'd find it too "girly". They started right away looking for another gift. But I brought up that boy right - he marched right up to the front of the church, grabbed it, and loved it. It still sits in pride of place in his bedroom, and even though he's a six foot tall teenager now, he's never once tried to hide it from his friends. I'm glad he's never felt he had to hate on "girl things" in order to feel confident about being a boy.