When will my AOL screen name stop working with iTunes?

Apple will stop supporting AOL Usernames after March 30, 2015.

Those using an AOL screen name to sign into the iTunes Store, App Store and iBooks Store are required to transition to an Apple ID. Once the account is transitioned, Apple services and purchased content associated with the account can be accessed using the Apple ID. If the AOL Username is not transitioned by March 30, 2015 access to purchased content will be lost permanently.