The seeds are sown much much earlier in life.
I'd agree with this as far as getting women and girls to come on board is concerned. The truly awful attrition rates for women in tech, though, we as employers have to take upon ourselves! Internalised attitudes of our female employees definitely don't help - but it's up to us as companies to recognise and handle this.
E.g., my firm runs dedicated trainings for female employees that cover stuff such as dealing with the nagging self-doubt, having to be twice as good to be noticed, reasons why women's careers fail ... you name it. In fact, the course is so feminist that some of the participants have complained about it being too Gloria Steinem in character (it's really a lot more Sheryl Sandberg, actually, but that's not the point).
We do need to do more in this regard. And this is up to C-level leaders on the one hand but also something I very much consider a responsibility of people like myself: lower and middle management that works with these women every day. And, yes, this may sometimes have to include coaching junior women into toughening up a bit - it shouldn't have to but it's the pragmatic approach to take. It'll also, however, very much include making it abundantly clear to male colleagues that sexism won't be tolerated - and follow through of they decide to ignore our directives.
So, yes, we do need to work with our girls to get them into Tech - but once we do we very much must have their backs still. It's simply no use wasting all those young women's years on a CS degree if we're not willing to see them as an investment worth protecting afterwards.
Rant over ...