word choice - Whats the difference between 成人 and 大人? - Japanese . . . 成人 is a very specific term and refers to persons who reached the age of 20 and above It's derived from the definition of the Japanese law, which says "年齢二十歳をもって、成年とする" You used to get drafted and taxed after this age In today's context, it's the legal drinking smoking age