Vice President of Sony Network Entertainment Eric Lempel recently took to the PlayStation Blog to announce PlayStation Network sub accounts can now be upgraded to master accounts.
PSN sub accounts allow users under the age of 18 to experience PlayStation content while a parent or guardian manages their access from a master account. Users who turned 18 or older were unable to upgrade their account until now.
Important information such as friends lists and trophies carry over in the upgrade process. At the moment it can only be initiated on the web, but Sony plans to introduce the feature to the PlayStation 4 as well. Further details can be found on the sub account support page.