Via one of the internal Atlassian blogs, I found Microsoft adCenter Labs Demonstration, which claims:
You can use adCenter technology to predict a customer’s age, gender, and other demographic information according to his or her online behavior—that is, from search queries and webpage views.
Admittedly, the small print at the bottom of the page says: "The statistics on this page are based on undisclosed size of sample data and are for proof of concept only. Actual results may vary." That said, they wouldn't be putting this up if they didn't think it was at least marginally accurate, right?
So without further ado. One of the screen-captures below is MSN's estimated age-distribution for you, my dear readers. The other is for popular children's site site Neopets.