Age of consent
The age of consent is the age in which it is legal to engage in sexual activity in a given jurisdiction. Most nations have an age of consent but in some cases such as the United States the age of consent laws are set by sub-national jurisdictions such as states. Engaging in sexual activity with a consenting partner that is under age is commonly known as statutory rape although the exact terminology will vary by jurisdiction.
Many jurisdictions have close-in-age exemptions in which sex is not illegal between people of similar age even if it otherwise would be. In some countries, notably the United States, these are called Romeo and Juliette laws.
In some jurisdictions, a defence can be asserted in which an adult genuinely believed that the minor they had sex with was of the age of consent or older. In Queensland Australia, for example the age of consent is 16 (except for anal sex, for which it is 18). The adult has a defence if they can demonstrate that at the time the offence occured they genuinely believed the minor was of the age of consent or older, so long as the child was actually 12 or older.
All else being equal men are far more likely to be charged with statutory rape than women so it is strongly advised that men establish the age of a potential sex-partner before sexual activity begins.