Close itunes, restart your computer, and then register in 2 hours. This time, you can fill in the age above 18 for the first time, because it is too late to upload iTunes related information after the computer restarts, so you can fill it in after the computer restarts.
What is the Apple id? Apple id is an authentication system introduced by Apple for its products. As a full-featured account, it allows users to access various resources of Apple, because an account can be used for a variety of products and services provided by Apple. It can also be called Apple account, MobileMe account, Mac account, iTunesStore account and iChat account.