Voting age should be a variable number.
Not everyone matures at the same age, and not everyone learns about being responsible and holding down job and raising a family and buying a house and trying to keep as much of their money away from the big government bureaucrats.
Mostly, people don’t all have the same knowledge-base and life experiences and time to grow some wisdom.
Some might be able to vote at 21, others at 30 or more, and others might never qualify to vote.
Too easy to screw over valid voters. I get the sentiment though.