While we're at it, maybe under-21s should have a parent's permission to enlist in the military.
Or vote.
If that state has an age limit of 21, it stands to reason parent would have to sign, as in getting married, joining military, or alcohol, etc. That is way it used to be, and still should be...I have not heard of laws stating it different. Wonder how many states are OF AGE AT 21? or 18? Is voting State law or Federal Law? Wikipedia says:
https://en.wikipedia.org/wiki/Voting_age
They can’t purchase a pistol?