I have googled around for the youngest Facebook user in the world, some registered their 3 days old baby and some even made an account for their unborn child. That obviously doesn't count because those babies can't even tell what a mouse is let alone update their statuses.
My 6 years old son on the other hand is a true blue Facebook user since, well yesterday. I created his account last year but he was too engrossed with Ben 10 and Spongebob to care. Flash forward today, after learning to watch music videos on YouTube and playing some games from Miniclip, Adam started to actually use Facebook.
He types his own status, approved his friends request, comments on people's updates and even chats with his uncles and aunts. Yesterday he spent over 2 hours with the computer using Facebook.
Okay now I only have to teach him some basic CSS and CISCO programming, then he'll be ready to take on the world.