The average age of consent in the United States is 16. In some states, it's 18. In some other states like Illinois and Missouri, it's 17. In some states, it's 14 for males. In other states, it's 16. The U.S. military's age of consent is 16 for both males and females. The age of consent for travelling American citizens abroad is 18. For example if an American citizen had sex with a 13-year old in Japan, he will return to the states only to be prosecuted.
I heard that a century ago, the age of consent in U.S. was ten years-olds.
http://www.spartacus.schoolnet.co.uk/REage.htm
In the 1860s the age of consent was twelve years old. Some people such as Josephine Butler and Barbara Bodichon were concerned that young girls were being sold to brothels. They became involved in the campaign against the white slave trade and in 1875 the House of Commons agreed to raise the age of consent to thirteen.
Campaigners were not satisfied with this change and continued to argue for further reform. In 1885 William Stead and Bramwell Booth of the Salvation Army joined forces to expose what they believed was an increase in child prostitution. In July 1885, Stead purchased Eliza Armstrong, a thirteen year-old daughter of a chimney-sweep, to show how easy it was to procure young girls for prostitution. Stead published an account of his investigations in the Pall Mall Gazette entitled Maiden Tribute of Modern Babylon.
In September, William Stead and five others were charged with unlawfully kidnapping a minor and committed for trial at the Old Bailey. Stead was found guilty and was imprisoned for three months in Holloway Gaol. As a result of the publicity that the Armstrong case generated, Parliament in 1885 passed the Criminal Law Amendment Act that raised the age of consent from thirteen to sixteen, strengthened existing legislation against prostitution and proscribed all homosexual relations.
http://en.wikipedia.org/wiki/Ephebophilia
Another society with tolerance for such relationships is Brazil, where ageism or prejuidicial treatment on the grounds of age has been forbidden by the Brazilian Constitution since 1998. In 1999, 28-year old Marcio Garcia, a nationally famous actor, dated 14-year old model Daniella Sarahyba for over a year in which period the relationship was accepted by the Brazilian mainstream media and by the television network which he worked for. Also in the 1990s 13-year old Kelly Key, who would become a famous singer, started dating 23-year old singer Latino, whom she married later on. Before that, in 1982, 40-year-old Caetano Veloso—a famous Brazilian singer and composer—began a relationship with 13-year-old Paula Lavigne, though he was already married at the time. He divorced and married Lavigne 3 years later. Their marriage lasted 19 years, ending only in 2004. The relationship was respected and he was not persecuted by the media or music industry. None were named as pedophiles, an accusation that could be considered as slander in Brazil.