What defines adulthood according to the chronological clock?

The definition of adulthood according to the chronological clock primarily focuses on the number of years since birth. This perspective typically sees adulthood as a stage reached when an individual attains a certain age, most commonly noted as 18 or 19 years in many cultures, although some societies may have different benchmarks. This age-based criteria is foundational to many legal structures, such as voting, drinking alcohol, and signing contracts, which are all tied to specific ages.

The other options, while relevant to the broader concept of adulthood, do not align with the purely chronological perspective. Physical changes from sexual maturity denote biological development but do not necessarily correlate with the societal definition of adulthood. Similarly, a mature way of understanding the world and the timetable of societal expectations relate more to the psychological and social dimensions of adulthood rather than its chronological definition. Thus, the key element defining adulthood in terms of a chronological clock is simply the passage of years, marking a transition into adulthood based on age.