Is this a DBWI?
People under 21 couldn't vote in the US for most of its history.
What I was wondering was whether demographics would make a difference. We would be enfranchising a lot of young people, so issues which would have been relatively important to the young would be more influential in elections.
At times it certainly would have made a difference one way or the other. For example, it's unclear whether Bill Clinton would have been elected if 18-21 year olds couldn't vote.