Marriage age in the United States

The marriage age in the United States is set by each state and territory, either by statute or the common law applies. An individual can marry in the United States as of right, without parental consent or other authorization, on reaching 18 years of age (and used to be 21 years of age before 1971) as that is the age of majority, in all states except in Nebraska, where the general marriage age is 19 as that is the age of majority and Mississippi, where the general marriage age is 21 as that is the age of majority. In Alabama, however, the age of majority is 19, while the general marriage age is 18. 
The minimum marriage age requirements of 12 years old for females and 14 years old for males were written into English civil law until 1753. By default, these provisions became the minimum marriage ages in the United states of America. English common law inherited from the British remained in force in America unless a specific state law was enacted to replace them. In the United States, as in most developed countries, age restrictions have been revised upward so that they are now (August, 2010) between 13 and 21 years of age. Prior to 1971, approximately 80% of states specified an age of 18 for marriage without parental consent for women, and approximately 85% specified an age of 21 for men.
When at least one of the marriage partners is under 18–21 years old, the marriage is considered an underage marriage and requires parental consent and/or judicial authorization. Also, adolescents can marry with "exceptional circumstances”. In many states (but not in Massachusetts), an adolescent's marriage automatically emancipates the minor, or increases his or her legal rights beyond allowing the minor to consent to certain medical treatments. In all but four states, couples are allowed to marry at a younger age with parental consent and/or with judicial authorization, with the minimum marriage age, when all exemptions are taken into account, ranging from 15 to 17. The states which ban marriage under 18 years old completely are Delaware, New Jersey, Minnesota, and Pennsylvania. In nine other states, a person over 21 years old can not marry a person under 18 years old.
History.
Colonial America.
Marriage law.
The minimum marriage age requirements of 12 years old for females and 14 years old for males were written into English civil law. By default, these provisions became the minimum marriage ages in colonial America. In England, the Marriage Act 1753 required a marriage to be covered by a license (requiring parental consent for those under 21) or the publication of banns (which parents of those under 21 could forbid). Additionally, the Church of England dictated that both the bride and groom must be at least 21 years of age to marry without the consent of their families.
Rape law.
In 1275, in England, as part of the rape law, the Statute of Westminster 1275, made it a misdemeanor to "ravish" a "maiden within age", whether with or without her consent. The phrase "within age" was interpreted by jurist Sir Edward Coke as meaning the age of marriage, which at the time was 12 years old. A 1576 law was created with more severe punishments for ravishing a girl for which the age of consent was set at 10 years old. Jurist Sir Matthew Hale stated that both rape laws were valid at the same time. Under English common law the age of consent, apart of the law of rape, was 10 or 12 years old and rape was defined as forceful sexual intercourse with a woman against her will. To convict a man of rape, both force and lack of consent had to be proven, except in the case of a girl who is under the age of consent. Since the age of consent applied in all circumstances, not just in physical assaults, the law also made it impossible for an underage girl (under 12 years old) to consent to sexual activity. There was one exception: a man's acts with his wife (females over 12 years old), to which rape law did not apply.
United States.
Marriage law.
English common law inherited from the British remained in force in America unless a specific state law was enacted to replace them. In the United States, as in most developed countries, age restrictions have been revised upward so that they are now between 15 and 21 years of age.
There are three sets of marriage ages: 1) general marriage, which is the same as the age of majority and 2) minimum marriage age by statute and 3) minimum marriage age by common law. There are threes sets of laws specifying minimum age requirements for marriage: 1) the minimum age with parental and judicial or court consent, 2) the minimum age with parental consent, and 3) the minimum age without parental consent. 
There is little variation over time or across states in the laws without parental consent. Prior to 1971, approximately 80% of states specified an age of 18 for marriage without parental consent for women, and approximately 85% specified an age of 21 for men.
In states without a legislated minimum, common law (which specifies a minimum of 12 years old for females and 14 years old for males) prevails; the estimated effect of a common law is similar to a legislated minimum of 13 or less (Massachusetts has the lowest legislated minimum in any of the 50 states, of 12 years old for females and 14 years old for males, but this is under the discretion of a judge and authorization must still be obtained from the Probate or District Court..) In California, a person under 18 years old can marry with parental consent but judicial approval is also required. California Civil Code (1872) "Males of the age of 18 years old and older and females of the age of 15 years old and older are capable of consenting to and consummating marriage." Section 56 of the California Civil Code (1872) fixed 15 as the age at which a female could marry without parental consent and in 1921 the age was raised to 18.
Rape law.
In Delaware, the age of consent was 10 years old until 1871 when it was lowered to 7 years old. The age of consent in question has to do with the law of rape and not the law of marriage as sometimes misunderstood. Under the 1871 law, a man was given the death penalty for sex with a girl below the age of consent.
In 1880, 37 states had an age of consent of 10 years, 10 states had an age of consent at 12 years, and Delaware had an age of consent of 7 years.
In California, early statutes forbid sexual intercourse with females under the age [25 Cal. 3d 618] of 10, following the English statute of 1576. In 1889, the California statute was amended to make the age 14 (Stats. 1889, ch. 191, § 1, p. 223.) and the age was raised to 16 in 1897 (Stats. 1897, ch. 139, § 1, p. 201.).
In the late-19th century, a "social purity movement" composed of Christian feminist reform groups began advocating a raise in the age of consent to 16, with the goal of raising it ultimately to 18. By 1920, 26 states had an age of consent at 16, 21 states had an age of consent at 18, and one state (Georgia) had an age of consent at 14.
Alaska was bought from the Russians and became the 49th state of U.S. in 1959. The age of consent was 16 years old. Hawaii became the 50th state of U.S. in 1959. The age of consent was 14 years old.
Two final states legislating their ages of consent into the 15–18 range were Georgia and Hawaii, from 14 to 16, raised in 1995 and 2001, respectively. One state (Colorado) had the age of consent at 15, having been lowered from 18 years old because age of majority was lowered from 21 years old to 18 years old in 1971.
In 2007, the age of consent was 18 years old in California and the age of consent was 16 years old in Massachusetts.
As of August 1, 2018, the age of consent in each state in the United States was either 16 years of age, 17 years of age, or 18 years of age.
In California, the age of consent is 18 years old and in Massachusetts, the age of consent is 16 years old.
Age of underage marriage by jurisdiction.
In the 50 states.
Every state except Delaware, Pennsylvania, Minnesota, and New Jersey allows a person under 18 years old to marry:
If one or more of the following apply:
Or in exceptional circumstances if one or more of the following circumstances apply:
In 6 states, a person who is 21 years old cannot marry a person under 18 years old - Missouri, Arizona, Colorado, Idaho, Louisiana, Nevada. In 1 state, Florida, a person who is 20 cannot marry a person under 18 years old. In 3 states, Georgia, Tennessee and Ohio, a person who is 22 cannot marry a person under 18 years old. In Indiana, this is also mostly true, although a person who is 21 can marry a person who is 17 years old.
Minimum age in 50 states:
From 2017 to 2019 several states changed their law to set a minimum age, or to raise their minimum age.
In Massachusetts the general marriage age is 18, but adolescents may be married with judicial consent. 
Unlike many other states, in Massachusetts an adolescent's marriage does not automatically emancipate the minor, or increase his or her legal rights beyond allowing the minor to consent to certain medical treatments.
In the territories and federal district.
Puerto Rico is a territory of the United States, and its people are American citizens. In Puerto Rico the general marriage age is 21 as that is the age of majority. The general marriage age in Puerto Rico is 21, however males aged 18 and females aged 16 can marry with exceptions. In Guam, the general age is 18, but 16-year-olds can get married with the consent of at least one parent or guardian. In American Samoa, since September 2018, the marriage age has been 18 for both sexes. Previously, the marriage age for females was 14. American Samoa does not allow underage marriages. In the District of Columbia the general age is 18, but 16-year-olds may marry with exceptions. In the U.S. Virgin Islands the marriage age is 14 for females and 16 for males. In the Northern Mariana Islands males must be 18 to marry, while females can marry at 16 with parental consent.