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Being at the age of majority—that is, old enough by law to vote, marry, or sign legal agreements without one's parents. Typically refers to age 18, the age of majority in the United States. Just because you're of age doesn't mean you're suddenly versed in the ways of the world—you're still just a kid. Our parents don't approve of the marriage, but we're both of age now, so they can't stop us.
old enough to marry, buy alcohol, or to sign legal agreements. (*Typically: be ~; Come ~.) Now that Mary is of age, she can buy her own car. When I'm of age, I'm going to get married and move to the city.
1. Old enough, according to the law, to be eligible for something, as in In this state he's not of age for buying liquor, but he may vote, or Next year Jane's coming of age and will get her driver's license. This usage was first recorded about 1430. The term under age signifies being too young to be eligible, as in It's against the law to serve alcohol to anyone under age.
2. come of age. Mature or develop fully, as in The school's bilingual program has finally come of age.