I'm aware the brain--especially the portion concerning planning and judgement--isn't matured until around the mid-20s and that the brain's structure is sensitive to environment. That said, let's assume a society with the knowledge of the adolescent brain being different from an adult brain educates adolescents early on personal and civic responsibility, and it's probably helpful to say the society doesn't stigmatize adolescent parenthood.
Would their brain maturation hasten in response to their upbringing, or would they at the least be more mindful of their thoughts and behaviors until they acquire the hardware some years later?
While I know of instances wherein mindfulness meditation have improved youth behavior, I didn't have any luck finding studies comparing the brains of adolescents with differing amounts of responsibility and mentoring. In addition, I know there will be individual differences, that some adolescents display better judgement than some adults, and that responsibility, mentoring, and judgement have a degree of subjectivity to them; let's say good judgement is the opposite of trolling and CZW Cage of Death.
Something else may also be said about the influence of collective and individualist societies.