It already is illegal here, which is kind of annoying as I am of age, but I don't have ID to back it up. So no R rated games for me. Unless I get my mother to buy them for me, which is just humiliating at this age.
John Lennon, 1940 - (Infinite Symbol) PSN: naathaann
Making it illegal to do so is the same as making it illegal to buy guns, and expecting crimes with guns to stop
It wouldn't stop them, especially not overnight, but it would drastically lower them eventually. Illegally acquiring them will become a lot harder and much more expensive when the people selling them run out of legal and easy options to get a hold of them. It's not exactly rocket science.
"When I became a man I put away childish things, including the fear of childishness and the desire to be very grown up. -C.S. Lewis