It's not that you have valid uses for your devices. It's that you trust yourself with the self-control to not to use the devices improperly or in ways that could be self-harmful, or, if so, to be able to bear the consequences. Adults can also drive, but children can't. There is no inconsistency there, either.

Writing as a parent who has had to deal with children staying up late at night, way after they should be sleeping, and looking up things on devices that I would consider inappropriate for both children and adults.