adult; person of full age
Formal or legal term for a person who has reached the age of majority. In everyday speech, 大人 (おとな) is more common.
In Japan, an adult was defined as a person aged 20 or older.
It is necessary to understand the rights and responsibilities as an adult.
未成年者 means 'minor' or 'person under legal age', the direct antonym of 成年者.
成年者 is the precise legal counterpart to 未成年者, denoting a person who has reached the age of majority.
minor; underage person
Compound of 成年 (せいねん, 'full age, adulthood') + 者 (しゃ, 'person'). The term is a straightforward Sino-Japanese construction.