"The reason 12-14 years olds seem immature is a social one, and NOT a brain one. I come from a rather different social culture and in my social circle a 12-14 y

"The reason 12-14 years olds seem immature is a social one, and NOT a brain one. I come from a rather different social culture and in my social circle a 12-14 year old was more or less an adult - and we acted that way. If you assume someone under 18 is a kid - they will act like a kid, if you assume they are an adult, they will act like an adult." That's idealistic, naive nonsense, for at least three reasons I can think of off the top of my head: 1) Take a six-year-old and start treating them as an adult and expecting them to act like one, and observe their behavior (my hypothesis: the child will behave like a slightly-more-mature-than-average six-year-old) 2) Do a survey of people who ran away or were kicked out of their houses at very early ages (let's say 15 or earlier) for traits and psychological health. (my hypothesis: you'll find significantly higher than average drug use, addiction, depression, and other psychological disorders than in a random population). 3) Take a forty-year-old male (who satisfies both of our criteria for maturity: my criterion that he has a fully-developed prefrontal cortex, and your criterion that society "assumes he is an adult" and treats him like one). Now remove his prefrontal cortex. Your argument hypothesizes that he will still be an adult, since the criterion that is important to you - society treating him like an adult - remains unchanged. However, this has actually happened many times. It's called a prefrontal lobotomy, and its effects are well-known - it basically turns an adult into a child. Therefore, the prefrontal cortex has much more to do with what we know as "maturity" than social treatment. (and if you want to be clever and say "well those who get a prefrontal lobotomy are usually severely retarded or mentally ill and thus not treated as adults before the operation," then just remember good old Phineas Gage. Treated as an adult right up until the railroad spike went through his head, and then basically became an impulsive child.) "(And you got downvoted for saying kids don't have a pre-frontal cortex which is nonsense, if you had said less mature I would have let it go.)" Wrong; it is a fact that children do not have a fully-developed prefrontal cortex. It can take as late as the mid-twenties to come online, and as late as the early thirties to fully myelinate. Social expectations have very little to do with capacity for long-term decision-making. It's biological - you either have the equipment or you don't. My argument is based on what we know about the brain and on experiments already performed or whose results will be pretty damn obvious; yours is an argument by assertion based on blank-slate idealism and one article in Scientific American Mind which you can't find. I know which way I'm betting, personally.