An adult; a grown-up — a person who is physically and socially mature, typically having reached the age of majority.
成人は選挙で投票する権利がある。
Adults have the right to vote in elections.
このイベントは成人向けの内容です。
This event is intended for adults.
大学生は法的には成人になる。
University students are legally adults.
Becoming an adult; coming of age — the process or event of reaching adulthood (e.g., coming-of-age ceremony).
二十歳のときに成人式に出席した。
I attended the coming-of-age ceremony when I turned twenty.
成人になると多くの法律上の権利と責任が生じる。
When one becomes an adult, many legal rights and responsibilities arise.