Been lurking for a while, figured this'd be a good place to make my first post.
I'm a trans woman (MtF). This isn't the first time (and it won't be the last) I've observed something about gender stereotypes just from having lived on both sides.
One stereotype that's widely known in the trans community is that a disproportionately large percentage of trans women work in tech (or are tech hobbyists). The "MtF CS nerd" is probably the biggest trans stereotype I can think of.
This stereotype doesn't extend to trans men (FtMs). In fact, it's assumed that the ratio of MtFs to FtMs in tech is about the same as the ratio of cis men to cis women in tech.
In the main online trans community I run in, where this stereotype is endlessly touted as being true (often tongue-in-cheek), most of us start our transitions somewhere between 18-45 and by and large is biased towards people who started in our twenties (I started at 28, myself, and I'm 30 now). People who started before or after that are really rare in that particular community (there are other communities that swing younger or older, by the way -- I'm just talking about the group I run with).
The only real conclusion is that whatever biased us towards or against careers in tech based on our perceived genders must have occurred in childhood, definitely before college and probably before high school as well. It probably happened in toddlerhood, really. There's an excellent SMBC comic on this, by the way, but I'm new and I don't know if posting a link will get this post tossed into the spam filter.
This is why I think putting pressure on companies to recruit more and more adult women is fundamentally flawed. There just aren't enough adult cis women who are interested, no matter how much any company tries to recruit. I'm also particularly appalled by attempts to demonize Linus Torvalds for not having enough women as core kernel developers: it's not his fault that people perceived as female (i.e. cis girls and pre-transition FtMs) are told as early as preschool that they shouldn't be interested in technology. Fix that part of society instead of demonizing project leaders.