That law is stupid and there's no way that the law is gonna pass or get enough votes to pass.
Many people under 21 have cellphones everywhere all over the world and they are very useful in emergencies for parents and teens and kids to contact each other.
For example what if that under 21 were being harmed or broke down on the side of the road and needed to call for help.
They would be worse off not being able to call for help.
The law about banning cellphones for those under 21 would be a bad thing so there's no way it's gonna pass.