Title: National Minimum Drinking Age Act
Content:  Legislation concerning the legal minimum drinking age in the United States can be traced back to the days of Prohibition. In 1920, the 18th Amendment to the U.S. Constitution declared it illegal to manufacture, transport, or sell intoxicating liquors. This was repealed with the passing of the 21st Amendment in 1933, which was followed by the adoption of minimum legal drinking age policies in all states, with most states electing a minimum legal drinking age (MLDA) of 21. Between 1970 and 1975, 29 states lowered the MLDA from 21 to 18, 19, or 20. This was primarily due to the 
Title: Legal drinking age controversy in the United States
Content:  The legal drinking age varies from country to country. In the United States, the legal drinking age is currently 21. To curb excessive alcohol consumption by younger persons, instead of raising the drinking age other countries have raised the prices of alcohol beverages and have encouraged the general public to drink less. Setting a legal drinking age of 21 is designed to discourage reckless alcohol consumption by youth, limiting consumption to those who are more mature, who can be expected to make reasonable and wise decisions when it comes to drinking.
Title: U.S. history of alcohol minimum purchase age by state
Content:  had raised their purchase ages to 21 (but not Puerto Rico, Guam, or the Virgin Islands, see Additional Notes below). South Dakota and Wyoming were the final two states to comply with the age 21 mandate. The current drinking age of 21 remains a point of contention among many Americans, because of it being higher than the age of majority (18 in most states) and higher than the drinking ages of most other countries. The National Minimum Drinking Age Act is also seen as a congressional sidestep of the Tenth Amendment. Although debates have not been highly publicized, a few states have proposed legislation to lower their drinking age, while Guam raised its drinking age to 21 in July 2010.
Title: Alcohol consumption by youth in the United States
Content:  Most states decided on the age 21 after prohibition, but the 26th amendment allowed individuals 18 and older to vote and serve in Vietnam, so several states lowered the drinking age as well. However, President Ronald Reagan, who was influenced by groups such as Mothers Against Drunk Driving (MADD) and Remove Intoxicated Drivers (RID), decided to federally enforce a 21+ drinking age by signing the National Minimum Drinking Age Act of 1984. He believed that doing so would decrease the number of accidents related to drunk driving, because he said that states with a drinking age of 21+ did not have as many drunk driving accidents. Reagan said that although he wished states would create their 
Title: U.S. history of alcohol minimum purchase age by state
Content:  from 21 to 18 in 1971 with the passing into law of the 26th amendment. Many states started to lower their minimum drinking age in response, most of this occurring in 1972 or 1973. Twelve states kept their purchase ages at 21 since repeal of Prohibition and never changed them. From 1976 to 1983, several states voluntarily raised their purchase ages to 19 (or, less commonly, 20 or 21), in part to combat drunk driving fatalities. In 1984, Congress passed the National Minimum Drinking Age Act, which required states to raise their ages for purchase and public possession to 21 by October 1986 or lose 10% of their federal highway funds. By mid-1988, all 50 states and the District of 
Title: Amethyst Initiative
Content:  The Amethyst Initiative states the following: "It’s time to rethink the drinking ageIn 1984, Congress passed the National Minimum Drinking Age Act, which imposed a penalty of 10% of a state's federal highway appropriation on any state setting its drinking age lower than 21. Twenty-four years later, our experience as college and university presidents convinces us that… Twenty-one is not working A culture of dangerous, clandestine “binge-drinking”—often conducted off-campus—has developed. Alcohol education that mandates abstinence as the only legal option has not resulted in significant constructive behavioral change among our students. Adults under 21 are deemed capable of voting, signing contracts, serving on juries and enlisting in the 
Title: National Minimum Drinking Age Act
Content:  states raised the minimum legal drinking age to 19 (and sometimes to 20 or 21). In 1984, the National Minimum Legal Drinking Act, written by Senator Frank Lautenberg (D-NJ) and influenced by Mothers Against Drunk Driving (MADD), required all states to enforce a minimum legal drinking age of 21 or else risk losing 10% of all federal highway construction funds. As the MLDA was still left to the discretion of the state, the act did not violate the 21st amendment which reserved the right to regulate alcohol for all responsibilities not specifically appointed to the federal government to the states. 
Title: National Minimum Drinking Age Act
Content:  The National Minimum Drinking Age Act of 1984 was passed by the United States Congress and was later signed into law by President Ronald Reagan on July 17, 1984. The act would punish any state that allowed persons under 21 years to purchase alcoholic beverages by reducing its annual federal highway apportionment by 10 percent. The law was later amended, lowering the penalty to 8 percent from fiscal year 2012 and beyond. Despite its name, this act did not outlaw the consumption of alcoholic beverages by those under 21 years of age, just their purchase. However, Alabama, Indiana, Kansas, Michigan, North Carolina, Pennsylvania, and Vermont, and the District of Columbia extended 
Title: U.S. history of alcohol minimum purchase age by state
Content:  the age in the table will read as "18", not "21"). In addition, the purchase age is not necessarily the same as the minimum age for consumption of alcoholic beverages, although they have often been the same. As one can see in the table below, there has been much volatility in the states' drinking ages since the repeal of Prohibition in 1933. Shortly after the ratification of the 21st amendment in December, most states set their purchase ages at 21 since that was the voting age at the time. Most of these limits remained constant until the early 1970s. From 1969 to 1976, some 30 states lowered their purchase ages, generally to 18. This was primarily because the voting age was 
Title: Mothers Against Drunk Driving
Content:  enacting of a 1984 federal law, the National Minimum Drinking Age Act, that introduced a federal penalty (a 5%—later raised to 10%—loss of federal highway dollars), for states that did not raise the minimum legal age for the purchase and possession of alcohol to 21. After the United States Supreme Court upheld the law in the 1987 case of South Dakota v. Dole, every state and the District of Columbia made the necessary adjustments by 1988 (but not the territories of Puerto Rico and Guam). However, in July 2010 Guam raised its drinking age to 21. In 1985, Lightner objected to the shifting focus of MADD, and left her 

Question: when was the drinking age set to 21?
Answer: By mid-1988.