To reach an age, 18 or 21 years, for example, at which one is no longer eligible for certain special services, such as education or protection, from the state.
法定年龄：到达一定年龄，例如18岁或21岁，不再享受国家的诸如教育或保护的某些特殊照顾
[usa. in imperative]behave in a manner appropriate to someone of one's age and not to someone much younger
行为与年龄相称
(of a person) reach adult status (in UK law at 18, formerly 21)
（人）成年（英国法律现规定18岁成年，原为21岁）
old enough to be able or expected to do something
到了…的年龄
the sons are of an age to marry.
儿子们到了结婚的年龄。
(of two or more people or things) of a similar age
（两者，多人，多物）年龄近似的
the children all seemed of an age.
孩子们看起来差不多大。