Playing games keeps you young. I grew up playing bridge and scrabble with my grandmother, who was an avid game player. She would play bridge every day if she got a chance. She kept her wits about her into her 90's!
These days I like to play the web game Scrabble Cubes, on Worldwinner, and I have even been known to play for money. Not a lot of social interaction, but its a calming break from the world and it does keep my mind sharp. (Or at least as sharp as I can manage)
The hubster plays MMOs - right now he's into Dungeons and Dragons online. I don't get into really complex PC Games. I figure if I am going to concentrate that hard on something I want to get paid for it. They make my brain hurt.
Of course hubster can beat me at almost any game. I think Scrabble is about the only game I can beat him at.