Is it that in order to enjoy computer and video games you need to grow up with them?
Perhaps, but I'd like to offer an additional explanation. I think that games are growing up as well, not in the sense of becoming more mature, but simply becoming, well, better, in terms of audio visual experience and the encompassing experience they provide.
(1984 - AlleyCat by IBM) AlleyCat could not catch the attention of a 20 years old like it can of a 5 years old. In order to capture the imagination of more mature people, complex games are needed. As games grow complex in graphics and content, so does the age group of the people who find them enjoyable.
In short, it's all about the effect of Suspension of Disbelief. As we grow older our Suspension of disbelief threshold grows with us. As the ability of games to draw us into their universes grew, so does the age of the people who are mesmerized by them.
This thought came up after a conversation I had with Shirley, regarding why I find theater boring in relation to Television or Movies; I had to excuse my lack of cultural sophistication to the fact that when I see theater, that's all I see: Actors, a stage, and a script, I never buy into it, because I've been exposed since the day I was born to mediums that suspend my disbelief much better.
It came to me that the same process takes place with computer games, after 3 days in a row that I spent all my free time playing Elder Scrolls IV: Oblivion, first time in years that I found myself drawn so powerfully into a game.
