It's not so much about skills (there are no skills that a 25yo hacking since 10 would have that a 55yo hacking since 40 wouldn't), but about selection: people w

It's not so much about skills (there are no skills that a 25yo hacking since 10 would have that a 55yo hacking since 40 wouldn't), but about selection: people who were more interested in computers than anything else at 10 -- and were spending all their time doing that, for absolutely no monetary or other reward, are going to be far better at doing programming (again, at any age) than someone who isn't that interested. And when there is an opportunity for such an interest to show, it would show early. Making sure that opportunity is there for most people would go a long way towards equalizing the gender ratios.