Why is the 18-25 year olds have underdeveloped brains meme pushed?

No.14379337 ViewReplyOriginalReport
>brain acts cognitively like an adult one by 15 and slowly grows into the role before that
>this actually can be tied down to biology
>however, many studies indicate that 'impulse control' is developing into the twenties
>this is thought by neuroscientists/psychologists to be tied to aging rather than environtment and circumstances/experiences as well as what certain individuals are more prone to
Not to mention, impulse control in the study that is often cited is apparently only developed fully by 2/3rds of adults by 30. By this logic, 33% of 30 year olds are dysfunctional (I wouldn't disagree)

Wouldn't this imply impulse control and decision making in the heat of the moment be tied more to experiences and upbringing and maybe more on the individual's traits? If 15 year olds can score on the adult range, clearly this could be the case?

Not to mention, according to certain anthropological studies, psychosocial maturity was reached much earlier than in modern times. What are the implications of this?