One of the positives of allowing the vote at 16 in Scotland (at least for local and Scottish Parliament elections) is that it gets young people into the habit of voting from a young age. 
I think it is positive to have a politically engaged population - even if not everyone votes the way you want them to 
Iirc, the English Higher was on 5 May 2016. Included in the paper was a as usual divisive article by Julia Hartley Brewer (for the critical reading question?), saying that they shouldn't be given a vote in the EU referendum as they couldn't think for themselves. By all accounts, it encouraged a lot of young people to go out and vote immediately afterwards
as there was a Scottish Parliament election that day 