What is the legal difference between 18 and 21?
<p>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.</p>

<p>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?</p>

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

<p>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?</p>

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

<p>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.</p>

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

<p>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).</p>

<p>There are many counties that prohibit purchase of alcohol at <em>any</em> age. The <a href="https://en.wikipedia.org/wiki/Ages_of_consent_in_the_United_States" rel="noreferrer">age of consent</a> 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 <a href="https://www.dol.gov/general/topic/discrimination/agedisc" rel="noreferrer">40 or older</a>.</p>

<p><a href="http://answers.google.com/answers/threadview?id=608781" rel="noreferrer">Here</a> 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.)</p>

<p>18 is explicitly invoked as the boundary age in Article 1 of the UN <a href="https://treaties.un.org/doc/Treaties/1990/09/19900902%2003-14%20AM/Ch_IV_11p.pdf" rel="nofollow noreferrer">Convention on the Rights of the Child</a>, 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.</p>

united-states minor