A 18 year old cannot fully understand the ramifications of going to war either. So why should Americans allow children to die for this country? They're allowed to put their life on the line, but the majority of the country would not do the same. I'm guessing you wouldn't, and that's the problem. People like yourself know if the age is raised to 21, the military would struggle getting anywhere near it's annual recruiting goal, and that's problematic for people like yourself.
Also, if you think all that training will get an 18 year old ready for the consequences of combat, including PTSD, psychosis, disfigurement, and biological or chemical warfare, then you might want to look in the mirror and see a real moron.
Btw, former 12B.