How do we define adulthood?

It’s odd that we can marry and vote before we can buy a drink.

Tin my home state of Connecticut is considering a bill that would raise the age of legal marriage to 18. Right now, like 26 other states, Connecticut sets no minimum age: 16- and 17-year-olds can marry with parental consent, and younger children — 15, 14, heck, 8 or 9 — can marry with parental consent and a judge’s approval. Between 2000 and 2014, there were 14 marriages in Connecticut involving 14-year-old girls.

As it happens, Connecticut is part of a trend. Eight states are considering similar bills, an explosion of interest due to the work of activist Fraidy Reiss, who entered into an arranged marriage with a fellow ultra-Orthodox Jew when she was 19, later divorced, and now runs a nonprofit called Unchained at Last.

Setting aside the merits of her movement — and I think there are many — the bill raises a larger question: Who counts as an adult? Our federal and state laws are an inconsistent patchwork of mixed messages. You can drive at 16 in most places, although not in New Jersey, where you have to be 17, or South Dakota, where you can get a license with some restrictions at 14 1/2. You can vote for president at 18, the same age at which you have to register for the draft. But if you are drafted at 18, you can’t have a beer after a rough day of basic training — you have to wait until you’re 21. Also at 18, you can buy a rifle or a shotgun from a licensed dealer — but not a handgun. For that, you have to wait until you’re 21.

Want to change these laws? You can run for the House of Representatives at 25, the Senate at 30, the presidency at 35. You can be mayor of most cities at a far younger age, usually 18, which means you could theoretically run a town without being able to drink in its bars.

These inconsistencies aren’t our countries’ most pressing problem. But our culture’s inability to agree on when adulthood begins contributes to some awfully infantile behavior, or at least our tolerance of it.

When the writer Charles Murray visited Middlebury College recently, students who disagreed with his views on race shouted him down, yelled obscenities, banged on windows, set off fire alarms and, after his talk, grabbed the hair of the professor who had debated against him. Some liberals said, in the students’ defense, “They are children!” That’s an odd way to think about adults old enough to vote and enlist in the Army, but perhaps a rational take on man-boys too young to drink.

We need to figure out who counts as an adult. It makes no sense to expect people to die for their country but not drink for their pleasure. By the same token, it’s absurd to say that people who aren’t old enough to vote are old enough to get married — if you can’t vote for town government, you shouldn’t be able to form your own household. There should be one age of majority when all of these rights are bestowed at once.

Of course, it’s not easy to determine the right age. Research suggests that our brains don’t reach cognitive maturity until we are well into our 20s — a strong argument for not letting 18-year-olds buy liquor or, for that matter, letting 18-year-olds drive cars or buy guns. Conversely, because 16-year-olds (and younger) can have babies, there’s a good argument for letting them marry the babies’ fathers, with the hope of creating stable families.

But the fact that any age of maturity we choose will necessarily seem arbitrary shouldn’t blind us to the common-sense wisdom of having a uniform one. Eighteen — when most people are done with high school — seems as good an age as any.

If we raise the marriage age to 18, and lower the drinking age to 18 — where it used to be in most states — then we’d have one meaningful age of majority for marriage, voting, drinking and military service.

Not to mention signing contracts. “We don’t allow children to enter into significant binding contracts before 18,” said Derek Slap, a Democratic legislator from West Hartford who said he’ll probably vote for the Connecticut marriage bill.

But what, I asked, about a couple of 17-year-olds who are truly in love? “Maybe once in a while Romeo and Juliet would have to cool their jets for a year,” Slap said. “But I am OK with that.”