I wanted to share what happened with us just yesterday. Oldest DS had a ped appt and youngest DS was there too. The ped has a PDA that has a program in it of all the different meds, dosage info, side effects, etc., that she pulled out to look up some information.
Both kids were like "oooh, what's that?"
So when she was done, she handed it to oldest DS. We were talking, and a few minutes later she looked over at him and he'd managed to leave the rx program and find the games and was playing checkers. Which, honestly, didn't surprise me much. She thinks he's real smart to be able to do that.

But this is the same kid that last year, his teacher used him as the classroom Tech Support. Youngest DS got hold of it, and although he stayed in the checkers game, figured out what to do no problem. I don't know much about PDA's, but it resembled a computer close enough they knew what to do, the only thing different was the stylus.
Of course, now they both want one.
Along with what Piper said, I think both kids could do those things about preschool age. About a year later, they also learned (by watching me) that when the computer locks up, to do the ctrl-alt-delete, which is not exactly something I wanted them to learn. And when the box pops up, how to figure out which program to exit to get the computer to un-freeze. (for example, we exit out of "iexplorer" and not just "explorer", cause exiting out of "explorer" means we have to completely restart the computer)
One thing I've taught them is aside from the games, using the internet for research purposes. Oldest DS caught onto that very quickly as a method for looking up game cheats. This is how you know you've crossed out of old fart status (LOL!)- when the kid asks you a question you don't know, instead of saying "go look it up in the encyclopedia", you say "google it"....