http://mashable.com/2008/05/15/youtube-demographic-data/

http://mashable.com/wp-content/uploads/2008/05/insights.gif

For now, you get a bar chart representing the percentage of your audience in different age groups, and a pie chart showing the breakdown of gender. You can then filter that data by country or for a specific time frame. Additionally, YouTube has rolled out aggregate data, so you can see the combined demographics for all of your videos. The data is all anonymous.