http://www.realage.com/
The test measures your "biological age" taking into account such factors as lifestyle, diet, exercise, habits. At the end it sends you an email and tells you your RealAge and explains what factors make your specific realage younger (such as good oral hygiene, no smoking) and what make your realage higher (such as low vegetable intake, high read meat intake). I don't usually take online tests but this was very informative and interesting. Didn't score as well as I'd hoped though.