When video games first premiered they were played primarily by the younger generation. As the gaming systems evolve adults can and will hog their kids games and many childless adults buy the systems for themselves. Along with lots of games.
The video game creators took notice and have brought out many games that are rated R or M, which means you need to be 17 or older to purchase these type of games. However with the internet and auction sites like Ebay, kids still get these games into their hands.
Thumbgods.com has posted a list of gaming systems starting with the first console Magnavox Odyssey down the most recent, which many people are actually waiting for and that is Playstation 3.