This tracks names by boys and girls based on popularity (birth) - type in any name and see the rise and fall. Using data like this it looks like you could predict someone's age +/- 5 years just based on the popularity of their name. Try it out with the names of people you know.

Very cool, you can't predict my age with it though. My name is Stuart, so judging by the spike you'd guess I was 50 to 60 years old; I'm 24.

Names visualizer (Java)