I feel as though age gates are useless and obtrusive. Any kid can pretty easily defeat the system by adding a few fictional years to their life, so they don't stop anybody from any 'mature content'. Plus, given the number of minors playing M-rated games, I'd say the system is largely unneeded--not only are companies not actually keeping people out, they're trying to stop the people who use their products.
OT: No, it's far more entertaining to come up with fantastic dates to get through age gates ('Why yes, I was indeed born during the American Civil War, why do you ask?').