In the Commonwealth of Massachusetts, the law regards 18-year-olds as adults. It presumes that they have the discernment and mental capacity to get married, to enter into binding contracts, to obtain a regular driver’s license, to work at any job of their choosing, to consent to medical or dental surgery, and to become registered voters. The law authorizes 17-year-olds to join the Massachusetts National Guard (or any other branch of the military). And it empowers 16-year-olds to take out an auto insurance policy or to get an abortion.

Yet if an 18-year-old breaks the law in the Bay State, dozens of Massachusetts legislators, among them Senate President Karen Spilka, believe that the offender should be regarded not as an adult but as a juvenile, exempt from normal prosecution and punishment for crime. It’s a bad idea in every respect.

The Globe reported last week on the ongoing project to enact “Raise the Age” legislation that would treat 18-, 19-, and 20-year-old criminal offenders as mere juvenile delinquents, except in cases of homicide. In January, 50 legislators signed on to a House bill that would make 21 the minimum age to be considered an adult for criminal-law purposes. That measure went nowhere (despite the celebrity endorsement of Boston Celtics guard Jaylen Brown). In July, the Senate tried a more limited approach; it tacked onto a $4 billion spending package an amendment hiking the age of criminal responsibility by one year, to 19. The amendment didn’t make it into the final bill, but Spilka seems unworried. “We have a good shot at getting it passed next session,” she told the Globe.

Let’s hope she’s wrong.

Raise the Age advocates make their case on purportedly scientific grounds. They maintain that it is unjust to allow lawbreakers who are still in their teens to be treated as adults by prosecutors and courts, given the evidence showing that the human brain isn’t fully mature until approximately 25 years of age. The prefrontal cortex, an area of the brain linked to executive functions, such as planning, decision making, personality expression, and moderating social behavior, continues to undergo changes into the early 20s. Thus there are biological reasons — so the argument goes — that younger people are less adept than older adults at suppressing the impulse to commit a crime. It is “unfair,” Spilka said, for young people “to be robbed of the opportunities to create a life full of meaning and happiness just because of an early entanglement with the criminal legal system.”

Yet there are serious problems with Raise the Age, beginning with the fact that the overwhelming majority of 18- to 20-year-olds don’t commit crimes. People at that age don’t always act wisely. But that means only that they are human, not that they are incapable of making rational decisions, resisting dangerous impulses, and abiding by the law. Public policy does not consider them juveniles because common experience confirms that they aren’t. It is incoherent to regard people in their late teens as adults for all the purposes mentioned above, yet indulge those who turn to crime as children.

It is also counterproductive. If you change the law so that more teens involved in shootings, vandalism, carjacking, or shoplifting must be treated leniently, it stands to reason that more teens will commit — or repeat — such crimes.

What reason predicts, empirical data confirms.

In 2013, Massachusetts expanded the juvenile justice system to include 17-year-olds, for the same reasons now being advanced to raise the age even higher. When University of Pennsylvania criminologists Charles E. Loeffler and Anthony A. Braga analyzed the impact of the change several years later, they found that the main effect had been an increase in recidivism — that is, repeated criminal behavior — for affected 17-year-olds. “Prosecuting older adolescents as juveniles,” they concluded, “can exacerbate rather than reduce future justice involvement.”

New York, too, learned the hard way that when teens are shielded from being prosecuted as adults for their crimes, more teens commit more crimes.

According to a 2022 New York Police Department report, the number of teenagers involved in violent gun crimes in the city tripled after the state legislature in 2017 hiked the age of criminal responsibility to 18.

“The Raise the Age law made it nearly impossible to prosecute 16- and 17-year-olds as adults, sending them instead to the Family Court system,” where serious punishment is extremely unlikely, the New York Post editorialized. Not surprisingly, the number of shooters younger than 18 jumped from 9 percent in 2017 to almost 13 percent five years later. Another study, by the New York City Criminal Justice Agency, found that nearly 50 percent of 16-year-old offenders were rearrested for new crimes in the first year once they could no longer be prosecuted in the adult criminal-justice system. Nearly as high was the recidivism rate for 17-year-olds.

In other words, despite the good intentions of lawmakers, Raise the Age laws operate as a revolving door. They let teens who have committed serious crimes return to the street, freeing them to commit new offenses — and hurt more victims.

To send the message that young people will face no serious consequences for their offenses until they turn 19 (or 20 or even 21) isn’t compassionate or enlightened but woefully misguided. It is better that the law catch up with them sooner rather than later, increasing the odds that they’ll face real justice and learn a tough lesson before it’s too late to turn their lives around.