The earlier the better. (Score 2, Informative)

I myslef am married with a 2.5 year old daughter. I must proudly say that she uses a laptop very well for her age. Just this past weekend my wife set up her laptop with the kid websites like Dora the explorer and a few others. My daughter navigated her fun and games sites like a champ. Yeppers, going to be another geek in the family. My wife is the one that keeps her grounded in everything else. Like social stuff and that sort of thing. I guess we teach our child what each knows best. I would have to answer your question with the obvious. When ever you think you want to buy/build your child's first computer. It's up to the parents and not anyone else.