Assertion: The insistence that even late 'teen-age human beings are "still really children" is one of the great canards of overprotective minds in modern day.
Example: It hasn't been all *that* long since a young man in Japan was considered adult at 15... certainly old enough to fight if he was of the military class. In the last ~60 years neither vote nor drink, much less the obligations of adulthood, are burdens placed on persons before the age of 20.
So when someone brings out that presumption of incompetence in those still living their second decade, you could point out all the good done by Americans of ages 18 and 19 who are by most measures functioning adults. The American Armed Forces are a professional volunteer force that values experience, but even in that environment, the average age of a soldier out on deployment barely cracks the low 20's.
you could simply point to examples of premeditated, competent, intention to do harm on a large scale, and note the accused is... 19 years old.
Which is it? Are they really all just children, some wayward, others led astray, others even kidnapped and brainwashed into being child soldiers; if society can just find a way to set them on the straight path they will be saved? Or are human beings competent at a far younger age than is generally accepted in modern society and thus should have both the privileges and punishments meted out to "adults"?