Some time in elementary, probably.
I know I attempted to play the NES when I was three. I actually remember being in some room of the old house (which we moved out of when I was 4 - I only have these awesomely distorted impressions of it left in memory, like a green couch that seemed fifty feet long), and my brother and/or cousins were playing Super Mario Bros 3, and he was racoon mario, and he was on one of the later-world floating levels where the camera moves automatically. Um
...
I later used, in elementary, some IBM computer with massive blocky text and wrote a story about a dragon who was a real starfish.
I know that I started using the internet when I was 9, and got a decent idea of what I was actually doing on the internet about 9 years after that.