Why is Age of Consent set at a specific age?

Question

Suppose a 15 year old girl is wed by her own parents to a 30 year old man and she gives her consent. In most US states this marriage will not be recognized and the man would likely be prosecuted for statutory rape.

On this Wikipedia says....

"Statutory rape laws presume coercion, because a minor or mentally handicapped adult is legally incapable of giving consent to the act."

But if her parents waited only a few months till her 16th birthday then all of a sudden her consent is recognized by the state and the marriage is valid and her husband is safe from prosecution.

Why do the states set a specific age?

Why don't they judge each marriage license application on a case by case basis (perhaps by interviewing the minor when their partner is an adult)?

Answer 1

I was initially going to vote to close this as a political rather than a legal question, however, I think there is scope for separating out the two dimensions.

Our society makes a distinction between children and adults by giving them different legal rights, obligations and protections. If you think about it, there are a lot of things beyond sexual activity where the law does this: voting, drinking, military service, compulsory schooling, legal culpability etc. What things are subject to legal restriction is a political distinction.

Now, there is no reason politically why these laws could not have been drafted to say "children can do this, adults can do that" and leave it to the courts to decide who is a "child" and who is an "adult". Biologically and emotionally people reach maturity at different ages so this is perfectly sensible.

It might even be more just. However, justice is only one thing that we require of our legal system.

Among the others are certainty and efficiency. Providing a bright line based on birth date gives certainty. Not requiring the court to deal with this on a case-by-case basis increases efficiency - justice is not free. This is why jurisdictions use age as a proxy for adulthood.

As to why they choose any particular age, that is a political question.

Answer 2

We set speed limits so we don't have to spend time fighting over whether you were driving too fast.

We put up fences so we don't have to spend time fighting over whose property you are on.

We set ages of consent so we don't have to spend time fighting over whether the child could consent to sex.

Answer 3

To have an effective law, there has to be a line drawn somewhere. Using age gives a measurable and objective line of what is and is not allowed. Using a standard like maturity might be more fair but is not measurable and very subjective and would make enforcement difficult and messy.

Answer 4

Child marriage is completely illegal only in Delaware and New Jersey, and is also redefined (upwards) in Nebraska and Mississippi. In a little over 1/3 of the states, there is no lower age limit. In Alaska, for example, those betweeen 16 and 18 can marry with parental consent, and those between 14 and 16 can marry with a court order. Arkansas does not impose any lower age on court-approved marriage.

So to some extent, most states do judge each marriage license application on a case by case basis, in particular for those who are below some statutorily set age – 18 most commonly, 19 in Nebraska, 21 in Mississippi. No state requires case-by-case judgment of those over 21. If there were no statutory limits, every marriage would be subject to case-by-case judicial approval. Such a move could have immense consequences for the concept of "rights". In the US, there are various fundamental rights, such as the right to contract, to drink, to marry, to vote, which cannot be freely abridged by the government. A law which curtails a right is subject to "strict scrutiny" meaning that it must addresses a compelling government interest, must be narrowly tailored to address that interest, and must be the least restrictive means of doing so. Subjecting all marriages to case-by-case judicial scrutiny would not survive strict scrutiny, nor would a law freeing all persons from contractual responsibility in lieu of a court order.

The typical age of marriage 18 aligns with the broader judgment that that is the age when individuals are capable of fully exercising rights and taking responsibility. There are numerous "case-by-case" exceptions that go both ways (e.g. a person over 18 may be declared incompetent; a person under 18 may be declared competent). The premise that there are no case-by-case exceptions is wrong. More narrowly, one would ask why in Alaska the lowest legal age for court-ordered marriage is not set at 13 years and 6 months, or 13 years and 4 months. Arkansas answers that question by saying "we let the judge decide".

This only addresses the question of age of marriage, as asked in the OP. Laws regarding statutory rape are even more nuanced (though they do not involve judicial pre-approval). Whether or not a foreign marriage is recognized in a state depends on that state's law. Washington state generally recornizes marriages that are valid in another jurisdiction unless the marriage is specifically prohibited, where bigamy and incest-related restrictions exhaust the legal limits.