The male characters from lots of war novels, movies are 18 year olds. Wars are fought by 18 year olds.
Quick story, in 2003, I was in the passenger seat of a Humvee, driven by an 18 year old kid, with a boot full of 18 and 19 year olds. The driver had never driven a car before landing in Kuwait. These kids were supposed to be among the first US personnel to the exterior 10 meter high sand berm separating Kuwait and Iraq, as part of that US invasion. His job was to drive us, while under artillery fire, on a cleared path through a series of minefields, swinging back and forth between the holes already punched in the two sand berms leading to that final one. Once there, the kids in the back would roll out, and get up that berm as quickly as they could, and one was assigned to look over the top and see what in the pre-drone world could be seen about the resistance. His job came with a life-expectancy of six seconds (meaning he'd be okay if he could survive those first six seconds). So, when it was time to leave, the driver, who was crying, grabbed some eye-black, using his thumbs, made a couple crosses on his cheeks, shouted, "Let's fucking do this" jumped in and drove like a bat out of hell. We might have spent half a second on the cleared path, but probably not. We drove at about 40 (racing in without a road) through minefields. In the end, he did a power slide into the berm, lifting the vehicle up on two wheels, the kids in the back used that to jump out and race up the berm. the kid with the "hope you can survive the full six seconds" job, scampered to the top, yelling "I am gonna die" and lifted his head over the top, fully expecting to have it shot off.
So, this is 18 year old males, in a nutshell. They can be idiots. They can be noble. They can be confused. they can be stubborn. They can be tragic and funny and horrible and fragile and strong. They can be, and often are, all of these things at the same time.
