Almost every movie these days will have a woman who is competitive. In action movies she will be a 100 pound waif who is capable of knocking out 250lb men with a few kicks. Or in less action oriented movies she'll be a super genius who shows up the boys with her brilliant deductions and knowledge. Look at Hermione - the nerdy, highly competitive role-models for millions of little girls. Girls idolize her but they typically do not take on her hyper-competitive nature because there is no need and a competitive mindset is usually caused by androgens more than anything.
Little girls are fed competitive female role-models constantly and are encouraged to be competitive. They are enrolled in soccer at a young age and encouraged to join leadership contests and writing contests and so on by schools, parents, and governments alike.
It's just completely not true that girls are not encouraged to be competitive. They are, to an extreme degree. The simple fact is that most girls quickly learn that it's a lot easier to get what they want by being beautiful, girly, and socially savvy than it is to spend hours hacking code.
As a 14 year old male nerd, if your computer is broken, you have no choice but to figure out how to fix it so you can play Quake or whatever. A 14 year old girl on the other hand learns that the easiest way to fix her computer is to get the nerdy guy to fix it for her. This is just simple economics.
Women who get into tech usually were raised by a parent who taught them to love technology/science for it's own sake. It takes an exceptional kind of parent to raise this kind of child though. Most kids don't have this - male or female.
One point to also consider, which I consider fundamental to any entrepreneur, be it tech or otherwise is the concept of "challenge". I think regardless of sex, if you really are challenged in an area, and feel like you can beat someone, or a company at their game, you will succeed.
More specifically, guys are challenged at a younger age, be it in athletics, video games, neighborhood ball, or your friends telling you, you're a wimp if you don't do this.
As simple as this sounds, guys thrive on challenges, we play video games for the challenge, and girls alot of times don't get that same oppportunity to be encouraged or challenged at a young age. Because this shapes the competitive drive and spirit of entrepreneurship. Sp, what I would say to the women entrepreneur question. Challenge, challenge, challenge. Doesn't matter when you start, embrace a good challenge.