Since the re-introduction of Compass in January 2016 it has offered adult only functionality, and all the youth data that was previously held on Compass has been deleted.
The deletion of youth data was necessary as it was becoming increasingly out of date and in the absence of youth functionality there was no way of maintaining or ensuring its accuracy.
The only reason for adding someone who is not yet 18 to Compass is to start the application for a disclosure check. (This may be necessary for example when they are planning to go to camp on / shortly after their 18th birthday.) For more details about this topic please see this FAQ.