I'm probably going to catch flack for this, but these posts are very ignorant.
My son started showing interest around 18 months, and i went with it. He started with Edubuntu which has a cool program that teaches basic mouse movements. When my daughter was a bit older she started showing interest, i started her off with Edubuntu as well.
Both of my kids now dual boot between Windows (for their games) and Edubuntu (for their learning).
We do set rules, that only allow them to play games for so long. If they are "learning" they can do it for as long as they want.
My son is now 4 and he helps the grandparents with their compters, so i get my holidays back.