under age

how can we sometimes try an under 18 year-old as an adult? i don't even understand how this is legal.

i know that turning 18 doesn't mean anything in the mental / psychological sense. some 12yo are more mature than many 25yo. but the law says that at 18 you are legally an adult. this means that you are mature enough to make decisions for yourself, like smoking, enlisting, gambling, anything sex related, quitting school, a tattoo... before 18 you're not allowed to make these decisions yourself, no matter how actually mature you are. it's kind of silly, but the law has to pick a age (since reviewing every single person for every single decision would take forever), and for whatever reason, they've picked 18.

i understand that with some gruesome crimes you want to try a 17yo as an adult. because mentally, 17 isn't too much different from 18. but you see the problem, don't you? it just keeps getting younger and younger. we've even tried 14yo as adults. 14!! that's too young to do anything! you can't drive, get a job, get married in most states (even with parental consent). and some states "have passed laws allowing a person who commits an extremely heinous crime such as murder to be tried as an adult, regardless of age." (source)

it's so strange. at 14 you're not allowed to get a tattoo (something that only affects yourself) but you are apparently mentally developed enough to decide to commit a crime and understand all the repercussions. oh, and btw, up until only 2005 was it still permissible for the govt to punish under 18yo by death.