My mother plays Solitaire occasionally. Maybe another card game but that's it. She does enjoy spending time on the Internet chatting to people on Facebook and some forums, though.
My father has been interested in games ever since we bough a PC and I used it for gaming (obviously). This was, ooh, like ten years ago or so. My father picked up Half-Life quite fast, I must confess, I thought keyboard+mouse navigation would confuse him a bit but they didn't. He learned the controls by watching me play so he never had "training wheels" so to say - he never used something simple to understand like the arrows for movement. He went straight for WASD. Other than that, he played HL2 and Quake 3. But he really likes strategies especially the C&C games - Red Alert 2 and Generals are his favourites. He also plays some browser games, or at least he used, to, I'm not sure he still does or at least if he does it as frequently.
Yes, as I said, my father surprised me with how fast and easy he picked up gaming, especially considering he hadn't really played anything before that (some really casual games with me when I was around 6 don't count I think). Well, he isn't a hardcore gamer, nor one of the best but that's because he likes the single player challenges a game brings, not competition necessarily.
Still a few times he managed to help me out with tactical advice about a game he practically saw 5 minutes ago. One of those times was when I was playing MechWarrior 4 and was being badly beaten at the beginning of one level. MechWarrior isn't the game you just look at once and "get" how it works, the way you might do with the majority of FPS. Another time he watched me play Medieval: Total War and within a few minutes (without me telling him anything, ) he understood enough about the mechanics and the flow of the combat to tell me where I made a mistake and what to do to own the enemy.