Starting March 23, 2013 you must be 14 years of age or older to enter the Disneyland and Disney World theme parks on your own. This rule will also affect all water parks at Disney World, Typhoon Lagoon and Blizzard Beach. Because children do not carry identification listing their age, cast members will monitor and question anyone alone who looks 14 or younger. The child’s parent or guardian would be contacted and required to come to the park to accompany them in.
This “new” age restriction brings consistency across the parks as there was not an age limit set at Disneyland and Disney World seemed to very from park to park.
A few more details can be found here on NBC News Travel Site.