1) Our military is largely composed of 18-24 year olds. We would be sending legal children to war.
2) The purpose of democratic voting is not to decide policy, it is to give legitimacy to policy decisions. When you disenfranchise a large number of people who believe themselves capable of decision-making, and who tend to disagree with the majority opinion, you risk revolts.
Note in particular the disastrous consequences of the product of these two issues.
18 is just fine.
It is emotional processing that goes undeveloped until the late 20's.
Emotion tends to trump cold hard logic -- especially in the young. Actually, hell, not just the young! I'm almost 30 and can't do any meaningful thinking if I'm emotionally upset about something.
I'm just saying, I'm not sure how much value I'd place on the logic of a 16 year old in something as emotionally charged as politics.
I think the overtly emotional nature of politics is exactly why it doesn't matter if you allow 16 year olds to participate. It's such an extreme that virtually all participants are affected, regardless of how much control they have over their emotions.
I wonder if lowering the voting age would shift the "young people don't vote" window lower, or if it wouldn't change at all because it's not that young people don't vote as much as it is that as you grow older you become more invested in your lifestyle and are therefore more likely to vote to protect/preserve/enhance/whatever it.
The problem is lack of information, not emotion. Politics is immensely complicated and hard to understand without the right heuristics, and, from what I've seen, age doesn't help here much at all. People just tend to believe whatever most in their bucket believe regardless of age or even education. Logic doesn't seem to do squat, which is actually not surprising if you think about it.
The idea that logical thinking predominates in voting for political candidates (even for people much older than 16) is distinctly at odds with reality; voting is very often driven by emotion and creating emotionally arousing appeals is a central element of political campaigning.
Responsible voting requires well-developed capacity for logical thinking and emotional maturity * and* the ability to integrate logic and emotion. The article describes 16 year olds as adult in the first of these areas, but not the other two. (In fact, it notes that people, in general, aren't adult in regard to dealing with emotionally arousing circumstances well into their twenties.)
Which isn't to argue against the idea of expanding the franchise to 16 year olds, but that's more because of the social benefits of their early engagement outweigh the costs of their potentially immature use of the frnachise than because they are fully mature in the respects relevant to voting (which, incidentally, is also true, IMO, of allowing 18 year olds to vote.)
After arguing on reddit with, presumably, lots of 16 year olds, I'm certain that there's more that goes into making informed voting decisions.