The site instructions are in Japanese, so read carefully!
1. Touch 'start'.
2. Wait for - countdown 3, 2, 1...
3. Memorize the numbers positions on the screen.
4. When the numbers disappear, click the circles from the smallest number to the biggest number.
5. At the end of game, computer will tell you the age of your brain
http://flashfabrica.com/f_learning/brain/brain.html
I managed to beat my real age by 30 years.