I think between 16 and 20 is acceptable, but I have one kid who turns 18 a week after the election. So will be almost 22 before they can vote in a presidential election. 19 or 20 before a local or state race.
So I think 16 makes more sense, because the national races being only every 4 years disenfranchises too many young people, everyone who is 15, 16, or 17 at this election won’t actually get to vote at 18.
My teenagers work and pay taxes.