I could accept the solution that the superuser decides about the age bracket of each regular user, that can be changed anytime. sudo chage -u mybob --bracket t

I could accept the solution that the superuser decides about the age bracket of each regular user, that can be changed anytime. sudo chage -u mybob --bracket teen Users cannot change the setting, it can be presented to apps and let parents simply and safely enforce will. The root is the ultimate leader of the system, let him do his thing.