Because that's when people get to vote. Suffrage has long been tied to adulthood and the age of majority in the United States. Before the passage of the 26th Amendment in 1971, 21 was the minimum voting age in most states—and thus served as the age of adulthood in most areas of law.
Most states have set the age of 18 as the age of majority. However, Nebraska (§43-2101) and Alabama have set 19 as the age of majority. Mississippi is the only state which has set the age of majority at 21 (S1-3-27).
The typical age of attaining legal adulthood is 18, although definition may vary by legal rights, country, and psychological development. Human adulthood encompasses psychological adult development.
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).
What do you mean by age under 21? The terms underage or minor often refer to those under the age of majority, but may also refer to a person under other legal age limits, such as the age of consent, marriageable age, driving age, voting age, etc. Such age limits are often different from the age of majority.
There is no universally agreed international definition of the youth age group. For statistical purposes, however, the United Nations—without prejudice to any other definitions made by Member States—defines 'youth' as those persons between the ages of 15 and 24 years.
middle age, period of human adulthood that immediately precedes the onset of old age. Though the age period that defines middle age is somewhat arbitrary, differing greatly from person to person, it is generally defined as being between the ages of 40 and 60.
Under most laws, young people are recognized as adults at age 18. But emerging science about brain development suggests that most people don't reach full maturity until the age 25.
adulthood, the period in the human lifespan in which full physical and intellectual maturity have been attained. Adulthood is commonly thought of as beginning at age 20 or 21 years. Middle age, commencing at about 40 years, is followed by old age at about 60 years.
The voting age was reduced from 21 to 18 in the year 1989.
About legal age in Australia
In Australia, you're considered to be an adult when you turn 18 years old.
There are different words for people in each decade of age: A person between 10 and 19 years old is called a denarian. A person between 20 and 29 is called a vicenarian.
Age does not a man make.
While the law says a boy becomes an adult when he reaches the age of 18, the measurement of manhood is not his age. Nor is it the size of his muscles, or knowledge, or even the amount of hair on specific body parts. I didn't understand what it was to become a man until after I had become one.
By 20 years old, a young person is usually considered an adult: their body size is fully grown, they can vote, get married, and many have already entered the workplace. But the evidence suggests that, by many important measures, adolescence continues until around the age of 24 to 25.
Biological, legal and social definitions
The United Nations Convention on the Rights of the Child defines child as, "A human being below the age of 18 years unless under the law applicable to the child, majority is attained earlier.” This is ratified by 192 of 194 member countries.
The United Nations defines youth as persons between the ages of roughly 15 and 24, with all UN statistics based on this range, the UN states education as a source for these statistics.
In the United States as of 1971, minor is generally legally defined as a person under the age of 18. However, in the context of alcohol or gambling laws, people under the age of 21 may also sometimes be referred to as minors. However, not all minors are considered juveniles in terms of criminal responsibility.
The concept that a person becomes a full adult at age 21 dates back centuries in English common law; 21 was the age at which a person could, among other things, vote and become a knight. Since a person was an official adult at age 21, it seemed to make sense that they could drink then, too.
Adulthood is divided into three stages: (1) early, (2) middle, and (3) late adulthood. Early adulthood starts at age 18 or 21 and continues until the mid-30s. During middle adulthood, people start to show signs of aging. Late adulthood is when most people retire from work and reflect on their life.
According to recent findings, the human brain does not reach full maturity until at least the mid-20s. (See J. Giedd in References.) The specific changes that follow young adulthood are not yet well studied, but it is known that they involve increased myelination and continued adding and pruning of neurons.
Our Prefrontal Cortex Becomes More Efficient
And throughout our twenties, it gets better and better at its job — not by growing, but by oiling the works, so to speak. Two things happen to the prefrontal cortex after adolescence ends: myelination and synaptic pruning, both of which sound frankly painful.
And 15 common traits of grown-up people.
Studies say men reach emotional maturity around 43, while 32 years of age is where most women mature.
Middle age is the period of age beyond young adulthood but before the onset of old age. The exact range is disputed, but the general consensus has placed middle age as the ages of 40 to 60.
When are we considered old? For women, the old age threshold is about 73; for men, 70.
Participants were divided into age groups that, broadly defined, covered young adulthood (18 to 35 years), middle age (36 to 55 years), and older adulthood (56 years and older).