I disagree. Various gender roles are pushed onto girls at an incredibly young age. Look at the boys and girls aisles at your local toy shop. We teach our boys to be builders and makers. We teach our girls to be designers and caregivers (at least in US stores). Our society tells many young girls that building stuff on computers is not a womanly thing to do.
That is of course changing as efforts are made to foster a desire to build in younger girls, but at least anecdotally that attitude hasn't hit mainstream.
Very few other professions has this. A plumber did not go around fixing pipes at age 10. A medic, while they might have played doctor, do not really learn any of the basic skills until hitting university education. The lawyer when he was 10 is unlikely to be reading law documents.
Beyond maybe the mechanic profession, what other professions beyond IT has this property?
If that's too cheap a shot, I believe most professional musicians began learning their instrument as children, though I struggle to find a source for that belief.
The medics I know personally:
* Volunteered in ER in high school -> Doctor
* EMT and high-hours babysitting in college -> Children's Therapist
Also, sports profession :-)
More anecdata: all of the best engineers I know came to it late, after doing other things first.
Actually, I would go so far as saying every profession with a high ratio of very passionate people and low-ish barrier to entry will exhibit something like this.
Sports are a magnificent example.
Also, the number of women historically majoring in CS dropped off significantly in the 1980s, when 1. Video gaming culture started to take off and 2. Hardware (something seen as more masculine) started to be emphasized more often. Like, programming historically was something women with math and CS degrees did, then I think there was a greater influence of hardware and tinkering with your hands that was part of being in tech. Stuff that is traditionally seen as more masculine.
The DSM-IV (1994) quotes a prevalence of roughly 1 in 30,000 assigned males and 1 in 100,000 assigned females seek sex reassignment surgery in the USA.
So there's a 3x factor feeding into that.
But the tech industry is also famously self-selective. Many people in the industry self-selected for it when they were pre-teens. Spending hours upon hours programming in BASIC or whatever on their C64s or TRS-80s before they were out of elementary school...before thoughts of sexism enter the consciousness. There is very little preventing young girls from getting involved with tech at a very young age except simple lack of interest.
Anecdotally, I remember growing up and horsing around with many friends on our 8-bit computers before any of us had 2-digit ages. As I grew up the friends and computers changed, but the basic demographic didn't. When my peer group hit puberty we would have killed a member of the peer group to get a girl involved in our group of nerds.
Many of my friends had sisters, none of their sisters cared the first thing about what we were doing. A few of their sisters showed some interest at times, but always seemed to have other priorities. This must be a shared experience as the type of group arrangement in the Big Bang Theory resonates with all of the tech industry males I know.
It wasn't until half-way through high-school that we finally lured a couple of girls into our group, but we spent most of the time teaching them basic computer skills than nerding out with them. Nevertheless I never heard anybody put the female members of our group down, or act like they weren't capable of eventually doing the high-nerd things that we were doing. To the person, everybody was helpful, and the girls hung around and one even tried her hand at majoring in CS...before changing majors to International Relations.
Happily, things have changed for the better. The number of women in tech has dramatically increased since those early days. It's not 50/50 by any stretch of the imagination. But there are actual women in tech these days doing cool things. They've self-selected to enter it and have put in the time to become good at it, and have managed to ignore the real sexism (such as it is) and that's very very cool.
It's an additional barrier that many males don't have to deal with, but I think self-selection at an early age is an even larger one.