Check this out. It will make you nuts! The instructions are in Japanese, so read these unless you know Japanese. It starts out easy and then becomes impossible. Some number people and those with freakish memories would find it all easy, I'm sure. That would not be me. My brain is around 34. It's ranged from 29-35.
1. Touch 'start'
2. Wait for 3, 2, 1.
3. Memorize the numbers positions on the screen, then click the circle from the smallest number to the biggest number.
4. At the end of game, the computer will tell you the age of your brain.