system
A chat on subreddit /r/PoliticalCompassMemes
human
There was a very extensive study done after WW2 that determined the ages they wanted in the fighting force.  While physically capable into their fourties, older men often would ignore or half ass orders that had more risk.  The age group of 18-26 was defined as the best balance between fitness levels and lack of maturity to be less likely to ignore orders of directly facing the enemy.

Long story short, they want them because at that age they're dumb and blindly follow orders to throw themselves at the enemy.  Which pretty much sums up our argument here, technically an adult, still probably very stupid.
gpt
Its their mistake to make - not the states