Comment by RandomGerm4n

The answer is quite simple. You just don't verify it. The point isn’t to verify the age but to set the age on the device itself. If the parents set the age on the cell phone or computer, that setting is then used as the basis. The operating systems can be configured so that only the device administrator can change the age. Systemd already has a field for storing the age, which programs can read. If the child doesn’t know the root password for the laptop, they can’t change the age. If they do manage to get around that, well, so be it. The solution doesn’t have to be perfect because it would still be an improvement over the current situation without restricting adults in any way.