Well I haven't read this whole thread, so I don't know where the discussion stands thus far. But I'll add my two cents.
I don't think it's right to say that an 18 year old can die for the country but can't have a say in how the country is run. The thing about voting is we each have our own reasons for voting how we do, and that choice reflects our current situation. An 18 year olds reasons shouldn't be discredited just because they're 18 and haven't had as many or the same life experiences as an older person. At 18 I think I was making more of an informed decision then most adults probably do when voting, and at 20 last November I felt the same way.
what you say is true.
one hundred years ago, 12 year old boys were considered adult, and were depended upon by their (most likely) family to help with the family farm. they understood the immediacy of their survival and knew they had a role in that. this being tasked with responsibility creates responsibility and maturity. today there is not that immediacy of survival, especially in the 'burbs. kids of 12 and on either side of that age are much more pampered, and much less likely to be tasked with being responsible, which leads to maturity. i once dated a woman who grew up early because her mom was a crack head, and the woman had to care for her mom, rather than the other way around. however, growing up early like that lacks the responsiblity as there is no model from which to draw examples for "being" save negative ones. the woman has issues, and i suspect she still does. she expressed a great deal of immaturity in her thinking.
age is the arbitrary criteria for assuming maturity, but the two shouldn't be harnessed irrevocably,
especially if there is fMRI evidence to show that the brains of under 25 ppl aren't mature. i do think when considering matters of supposed importance such as deciding the direction of the nation/state/municipality, maturity rather than age should be the criteria. i say supposed because we are handed picked candidates by those who are in power (the monied elite) and so our real choices are narrowed to be almost useless.