http://www.youthrights.org/issues/voting-age/voting-age-status-report/
Though the Cambridge, MA city council in 2002 passed 8-1 a resolution to allow 17-year-olds to vote in municipal elections, it has gone nowhere. Not to be too cynical, but if 16- and 17-year olds could vote, it would be harder for state legislators to pass, say, restrictive driving rules or higher insurance rates for drivers younger than a certain age.
But we already have a myriad conflicts of interest like that. Police officers can vote, and police unions make it difficult to pass meaningful criminal justice reform in some places. Teachers can vote, and that sometimes makes it hard to make changes to the school system. Business owners can vote, so that makes it hard to pass necessary regulations on business. And the list goes on and on.
I get what you're saying, but there is another side to that as well. For instance, 16 year olds can't vote, so they can't influence lawmakers to better fund their schools.
edit: just realized the age of this post/thread
