>1. I can just as easily claim that most of those companies are owned by old people.

Yes, you can. I would argue that being older means that you have had the time to accumulate skills, experience, and connections. What does being a man give you? Upper body strength?

>2. Same reasoning as above.

I missed that reasoning. Most companies are owned by old people (something that I'm not even sure is true), therefore there's no sexism?

The point I was trying to make is that in the times many of those companies were created, sexism WAS a legitimate issue, which means that most of these companies are run by men. Nowadays, it is not nearly as big an issue as it is made out to be, but that does not magically infuse the old companies with 50% women. This is why using this statistic is inherently flawed, as the companies were simply created in a different time (if you don't believe me, check http://money.cnn.com/magazines/fortune/fortune500/. Very few of those companies are what you would call nouveau riche).

I would argue that the age of the company isn't what's important, but the age of the CEO. If a 150 year-old company has a 45 year old CEO, what does the age of the company have to do with it - unless you are arguing for long lasting traditions of discrimination that are invariant for a company.

Large companies tend to have a fair amount of nepotism in the top ranking positions. You would have to control for this as well.

Women would benefit from nepotism.

would? You mean they do? http://en.wikipedia.org/wiki/Gina_Rinehart