In 1875, England raised the age to 13 years; an act of sexual intercourse with a girl younger than 13 was a felony. In the U.S., each state determined its own criminal law and age of consent ranged from 10 to 12 years of age. U.S. laws did not change in the wake of England's shift. Nor did Anglo-American law apply to boys.
...
At the end of 19th century, moral reformers drew the age of consent into campaigns against prostitution. Revelations of child prostitution were central to those campaigns, a situation that resulted, reformers argued, from men taking advantage of the innocence of girls just over the age of consent.
...
The outcry it provoked pushed British legislators to raise the age of consent to 16 years, and stirred reformers in the U.S, such as the Women's Christian Temperance Union, the British Empire, and Europe to push for similar legislation. By 1920, Anglo-American legislators had responded by increasing the age of consent to 16 years, and even as high as 18 years.
...
Opponents remained focused on physiological maturity, however, and argued that girls in their teens were sufficiently developed not to need legal protection. Moreover, they argued, by late adolescence girls possessed sufficient understanding about how to use the law to blackmail unwary men.
...
In the 1930s, support for setting the age of consent at 16 years or older began to weaken. Characterized by growing economic, social, and cultural independence, girls in their teens assumed a place in western societies quite distinct from that of younger children. New concepts of adolescence and specifically of girlhood normalized sexual activity during the teenage years, at least within peer groups, as "sex play" necessary to achieve adult heterosexuality. Emboldened and influenced by such ideas, girls more often talked of being "in love" with the men charged with having sex with them, and expressed sexual desire. Prosecutors and juries increasingly refused to treat such cases as rape.
Legislators, however, did not reduce the legal age of consent. The resulting tension was reflected in slang, most notably the American term "jailbait," dating from the 1930s, that registered cultural recognition of teenage girls as sexually attractive, even sexually active, but legally unavailable. American legislators did amend laws to take account of the offender's age during the 1940s and 1950s as teen culture expanded and female adolescents exercised their sexual autonomy. During and after World War II, if both the male and female were underage (or between two and six years above the age of consent), the punishment was reduced.