He's been using the computer since the age of 2. I taught him how to move the mouse around the screen at that age teaching him up, down, left, and right.
Now, aged 3 and 3/4, he listens to my ipod playing edutainment games on Knoppix Linux. I totally recommend Knoppix Linux for the educational software provided on the Live CD. Aimed at the 2-10 age group. Being a Live CD, it just boots from computer boot up, and does not damage any thing on the hard drive. No need to install anything.