What two reasons does the author of what the brain says about maturity give to explain why brain development is not used to determine when adulthood begins?

The author notes that brain development does not determine adulthood because maturity encompasses more than just brain growth; it also involves emotional and social factors that influence decision-making and responsibility. Additionally, societal and cultural norms play a significant role in defining adulthood, which vary across different communities and time periods, making it difficult to rely solely on biological markers for such a complex transition.