Rather than looking at the math ability distribution as a proxy, why not look at coding competition ability? They are pretty objective since an autograder doesn't know your gender and they are predictive of whether you can pass a tech interview since it's the same format.

In that case, even at the IOI level (high school, so 14-18 year old kids) women are already severely underrepresented: https://www.quora.com/How-has-female-students-participation-...

You see the same thing at the college level too (for example topcoder where they isn't even any possibility for a sexist team selection bias since anyone can just register and compete).

In some sense, it makes it not tech industry's fault. It's a failure of our education/training pipeline where we are not training competitive women even from an early age.