成年(せいねん) せいねん noun adulthood, legal age See also: 青年(せいねん) (youth) 1. adulthood, legal age, majority The age at which a person is legally considered an adult with full rights and responsibilities. 日本(にほん)では成年(せいねん)は18歳(さい)だ。 In Japan, the age of majority is 18. [Note: Changed from 20 to 18 in 2022] 成年(せいねん)に達(たっ)すると選挙権(せんきょけん)が得(え)られる。 When you reach adulthood, you gain the right to vote. 成年(せいねん)後見人(こうけんにん)が必要(ひつよう)な場合(ばあい)もある。 There are cases where an adult guardian is needed. 成年(せいねん) is a legal term referring to the age of majority. In Japan, this was lowered from 20 to 18 in April 2022.COMMON TERMS:成年(せいねん)に達(たっ)する: to reach adulthood成年(せいねん)後見(こうけん)制度(せいど): adult guardianship system成年(せいねん)後見人(こうけんにん): adult guardianOPPOSITE:未成年(みせいねん): minor, underage personNOTE: This is a homophone with 青年(せいねん) (young person, youth). Related Words Antonym: 未成年(みせいねん) (minor) Related: 青年(せいねん) (young person) general Added 2026.1.13 8:49 · Revised 2026.5.12 0:21 00000/00456_seinen