In the case of games, it is purely advisory from a legal context (IANAL). However, many major (brick-and-mortar) retailers refuse to sell M-rated games to anyone under 17 or 18 years of age in the US.
paulraps writes "More bad news for The Pirate Bay. A week after a prosecutor announced charges against the file sharing site, hackers have stolen a list of all 1.6 million usernames and passwords for registered users, reports The Local. The group calls themselves "Angry Young Hackers" and they first hit the headlines when they defaced the website of Sweden's Anti-Piracy Bureau. So now nobody knows whose side they're on. Meanwhile, The Pirate Bay is urging users to change their passwords immediately."