My son is starting young on his geek life. At the age of 3 yrs old, just give him a computer and he will know his way around whether he is using Windows or Linux.
As of now, he has his own old Dell Inspiron 2500 laptop. But I have to keep on hiding his laptop from time to time because of addiction. Trying to keep him in touch with the real world. There are times when I woke up 1:00 AM in the morning only to see my soon glued in front of his laptop.
Now, me and my wife tries to give him a balanced child life by playing outside and of course using his beloved laptop.