It depends on the child and their environment, I would hazard a guess at saying that any child brought up in a home where parents are going to show them a unix

It depends on the child and their environment, I would hazard a guess at saying that any child brought up in a home where parents are going to show them a unix terminal is definitely going to be literate enough already. Many others would be, too. (At 5, certainly - 3 I know less about..)