Well, 16+ voting isn’t novel – lowering the age has been happening a lot recently in various parts of the world.
I’m not trying to convince you – and I didn’t even KNOW it was “a thing” ’til last night. But it’s interesting http://www.fairvote.org/reforms/right-to-vote-amendment/lowering-the-voting-age/
Also, Washington D.C. just means that: City of Washington D.C but larger areas in different parts of the world have already switched.
It allows them to discuss the issues while they’re still in school too – something to consider. When they’re out of school, out of reach of mandated adult influence… they’re on their own, alone, and easily manipulated with nobody to say, “Um… no.”