Missouri teens want to lower the voting age to 16 in local and school elections
(news.stlpublicradio.org)
Sure, and this is another gradation of voting; this would only be for local and school elections, which can have pretty immediate consequences for teens. In fact, 16 year olds (and others around that age) are the best positioned to have a say about school board policy, because they have been and currently are directly affected.
I do appreciate your perspective that a 'stepwise' system of adulthood can have huge benefits. I think this proposal actually fits quite nicely into it. They aren't voting for president; they're voting for the who will run the place they spend 8 hours per day.