I know at 18 someone is no longer a minor. But what is the reason for someone not getting full legal rights until 21? Examples: Alcohol, tobacco, etc.

What gives the government the power to allow a 21 year to do something and forbid it for an 18 year old, since neither is a minor?

For example, could a state legislature pass a law revoking a peoples right to drink at 50?

In summary what I am trying to get at is what is unique about the age 21? Or can the government restrict rights at any arbitrary age?

  • In the US it follows from the National Minimum Drinking Age Act of 1984 (passed to reduce drunk driving), which inspired states to preserve their highway funding by lowering the drinking age.
    – user6726
    May 5, 2016 at 17:26
  • 2
    Errh, yes, raising. I get those two confused sometimes.
    – user6726
    May 5, 2016 at 18:04
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    Years ago I walked into an adult store in NY and was asked to see ID. I asked how old you had to be to enter and was told 21. So I asked, "Are you telling me you have to be 18 to star in an adult film, but 21 to watch it?" She looked surprised, but we had a good chuckle since apparently that's the case.
    – TTT
    May 6, 2016 at 14:08
  • "For example, could a state legislature pass a law revoking a peoples right to drink at 50?" At least one state has had a bill introduced in the legislature that cleared at least once house of the legislature that would have done that for tobacco, although I don't believe that it became a law, and there was no serious doubt that it was constitutional to do so.
    – ohwilleke
    Jul 12, 2019 at 0:22
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    @TTT If someone were prosecuted for violating that law while age 18-20, there would be a legitimate argument that the law should be struck down for violating the constitutional "rational basis" test. Very few laws indeed fail that test, but this conceivably could be one of them, since the greater ought to imply the lesser. A CA statutory rape law was once struck down using similar reasoning.
    – ohwilleke
    Jul 12, 2019 at 0:25

2 Answers 2


I think your confusion stems from assuming there is a universal definition of "minor" across laws, jurisdictions, and rights.

18 is the age of majority for the purpose of voting (26th Amendment), the death penalty, labor law (although age 14 is the minimum age for employment), and many other laws.

But, 21 is the age required to buy alcohol in all states (by their own choice in order to receive highway funding).

Nothing requires the age of majority to be consistent across different sections of code or statute or between jurisdictions (except when constitutionally prescribed, like voting age, or minimum age for certain elected offices).

There are many counties that prohibit purchase of alcohol at any age. The age of consent varies between 14 and 18 across US states. Age 65 is a threshold for certain tax credits. You need to be 25 in order to be a member of the US House of Representatives, 30 to be a Senator, 35 to be President. You are only protected from age discrimination if you are 40 or older.

Here is a rough list of various age-based thresholds for various rights, privileges, or responsibilities in the US. (I havn't vetted this whole list, and some are clearly satire, but the ones I know about are consistent with my understanding.)

  • Interesting list - you can wear red lipstick at age 35, and no mention about aging out of Selective Service registration at 25...
    – user662852
    May 5, 2016 at 22:30
  • "You are only protected from age discrimination if you are 40 or older": only for employment. That doesn't prohibit age discrimination against those 40 and older in other matters.
    – phoog
    Jul 10, 2019 at 18:23

18 is explicitly invoked as the boundary age in Article 1 of the UN Convention on the Rights of the Child, so it is binding to a large number of signatory countries all over the globe under treaty law. The significance of the age of 21 varies much more widely between jurisdictions.

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    The USA has not ratified UNCRC, so this is irrelevant to the question and not an answer at all.
    – user4657
    Apr 4, 2018 at 4:26
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    USA has, however, in 2002 ratified two of its optional protocols, which for obvious reasons define the concept of child, and they both also invoke the age of 18 years as the boundary criterion.
    – dig
    Apr 4, 2018 at 4:52
  • But the optional protocols apply only to limited circumstances. One applies to armed conflict, and the other applies to human trafficking, prostitution, and pornography. It has no bearing on the legal definition of majority, nor on the application of age-based restrictions to those who have attained majority. Furthermore, the convention does not obligate any jurisdiction to recognize 18 as the age of majority. In fact, it allows jurisdictions to remove people from its protection by granting them majority before their 18th birthday.
    – phoog
    Jul 10, 2019 at 18:19
  • A jurisdiction is also perfectly in compliance with the convention if it sets the age of majority above 18, but minors who are 18 years old or older will not be considered "children" under the convention, and will also therefore lose its protection.
    – phoog
    Jul 10, 2019 at 18:20
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    This seeks irrelevant, since the UN is not a government and has no real authority over its members.
    – Andy
    Jul 10, 2019 at 22:32

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