Ping.
The right of citizens of the United States, who are 18 years of age or older, to vote shall not be denied or abridged by the United States or by any state on account of age.
What makes it clear to me is watching as teachers in the local school district ensure 18 year old students are registered, and then making the local high school a polling place for school bond levies.
It may be legal, but it is not ethical. I can't take someone off the street, get them to a polling place and go into the booth with them to instruct them how to vote.
With only minor differences, that is what is taking place with the teachers and students as described above.
Legal plunder of property owners. Beyond this specific instance, 18 year olds have not formed a sufficient world view on their own to vote responsibly.