Well, it was a very interesting experiance. I expected it to be much slower and more difficult.
I knew that my grandfather used to some Risk with us once in a while, so I guessed the Turn Based Strategy idea could work. To my great surprise, it did very well. I presented my grandfather with Civ IV, as you have suggested. I thaught I would then spend eight hours trying to teach the old man about the "Mouse" thingie and how you are not sussposed to actually touch the screen with it, but grandpa learned everything very quickly. I helped him get a little into the game, explained in abstract terms the ideas behind some alien concepts(It turns out some things we kind of take for granted about strategy games actually make no sense at all for a new person). At the end of the day, he found the game to be rather charming, even if he still needed help doing some things. I guessed he had the right mind for strategy like that. Some old people are really intelligent.
Over all I belive this "lesson" went extremely well, much better than I had expected. We will do it again some other day. For now, I am happy that I gave my grandfather a few amusing hours with a new, intriguing hoby in potential.
As for flight simulators, I will wait a little before showing him those. He is a healthy man, but he is also quite old. I kind of doubt that he still has the reflexes and the coordination to do well on such a game, and I don't want to frustrate him to much at this time.
Thank you all very much. You were very helpful.