A cool mind test from Chris:

1) Click the link below:
2) Most of the website is in Japanese, ignore that. Click "START".
3) Wait for the 3, 2, 1 countdown. At the end of the countdown, various numbers will flash in the box.
4) Try to memorize the positions of the numbers and, when the circles appear, click on the circles in order of the numbers, going from lowest number to largest number. At the end, the age of your brain will be displayed.

My brain is somewhere between 29 & 32 years old, which is pretty good since I'm 31 (and a half!!). I played twice and got 29 on my second shot.