I often see people assuming that sex with under-18-year-olds is a crime (statutory rape); for instance, some comments on the 17-year-old gets help in lying about age to get abortion; later, she and her mother sue helper (the boyfriend’s mother) for providing the help thread assumed that the sex must have been a crime — though the age of consent in Indiana, the state where the sex likely took place, is 16. Indeed, the great majority of states set the age of consent at 16 or 17, and many states set even lower ages of consent where the parties are close in age to each other.

1. Let’s start with what I call the “general age of consent”: The age at which it’s not statutory rape for anyone (except a relative or someone in a particular sort of position of authority) to have sex with the person. Let’s also focus on male-female vaginal sex; some states may still have different ages of consent for same-sex sexual contact, and possibly for oral or anal sex — I’m just not sure.

As best I can tell, 30 states set the general age of consent at sixteen; 8 set it at seventeen; and 12 set it at eighteen (though it’s possible that the last there are actually 7 at seventeen and 13 at eighteen, because of an odd twist with Texas law). The age-16 states tend to be smaller, so a little less than half the population lives in those 30 states. Over 60 percent of the population lives in the states that set the age of consent at 16 or 17, regardless of how one counts Texas.

Nor is this some purely modern invention. The ages of consent throughout the country were apparently 10 or 12 throughout much of the 1800s; they then rose to 16 or 18 by 1920, according to Mary Odem’s “Delinquent Daughters: Protecting and Policing Adolescent Female Sexuality in the United States, 1885-1920,” and there have been minor fluctuations since then. The last state to raise the age of consent from 14 to 16 was Hawaii, in 2001. Moreover, until recently the statutory rape laws applied only to girls, not to boys; heterosexual sex with an underage boy wasn’t statutory rape at all — now it is.

2. On top of that, many jurisdictions have so-called “Romeo-and-Juliet” laws that lower the age of consent where the parties are close in age to each other. For instance, D.C. sets the age of consent at 16, but as best I can tell excludes situations where the difference between the two parties’ ages is four years or less. (Given how Romeo and Juliet ended up, I’m not sure “Romeo-and-Juliet” is the most auspicious label here.)

3. An age of consent of 16 may seem very low to you. If that’s so, you may be shocked to know that — according to the accounts I’ve seen (e.g., here) — it’s 13 in South Korea and Japan, and, until recently, Spain; 14 in Austria, Germany, Italy, and Portugal; 15 in Denmark, France, and Sweden; and 16 in most of the rest of the Western world. The age 17 and 18 states in the United States are outliers, though Ireland and a couple of states in Australia are also at 17.

Now one can certainly debate what the age of consent ought to be. But one can’t just assume, reading a story about a 16- or 17-year-old having sex, that “17 will get you 20” and that the sex had to be statutory rape; to figure that out, one would need to look into the age of consent in that jurisdiction, and likely also consider the relative age of the parties.