correction

This article originally gave incorrect figures for the proportion of the American population that are in their teens and early twenties — and for the proportion of gun crimes that population commits. The figures have been corrected. It also said that Robert Aaron Long, the suspect in the Atlanta mass shooting, was 23 at the time of the alleged crime. He was 21.

When I was 16, some friends and I snuck out of school at lunchtime to go to McDonald’s on a rainy day. We had less than an hour to accomplish our mission, so I was rushing — and frustrated to find myself behind a slow-moving car. Even though I knew the treads on the tires on my dad’s sedan were worn, with all my six months’ experience on the road, I tried to pass on a two-lane road.

We hydroplaned at 55 mph and hit an oncoming car. My dad’s car was totaled, as was the car we hit. Everyone was wearing seat belts, and remarkably, no one was severely injured, although my best friend’s head cracked the window, and I think I lost consciousness for a couple of minutes. But had things gone differently, my poor judgment and impulsive act could have killed several people.

Whereas many of us know the dangers posed by young drivers, a key risk factor that has received too little in discussions of gun violence is age. People between the ages of 14 and 24 constitute just over 16 percent of the population in the United States, but they commit nearly half of the murders — and most use firearms. The pattern of murder offenses by age shows a clear arc: It rises sharply in the late teens, peaks between the ages of 20 and 24, and then begins to decline.

There are developmental reasons people in their late teens and early 20s, especially males, are particularly likely to engage in gun violence and other dangerous acts (like my reckless driving). A crucial factor is that the frontal lobes — which help us think through our actions — do not fully mature until roughly age 25. There is, moreover, another brain-development issue relevant to mass shootings in particular: The teens and early 20s are a crucial window for the onset of severe mental illness, particularly psychotic disorders such as schizophrenia. That window begins to close around age 25.

These facts open the door to a gun-regulation compromise. Even if more aggressive measures are stymied by gridlock, Congress might consider banning the sale of firearms to people under 25 (except, perhaps, hunting rifles). Even conservatives have shown some appetite for age-based restrictions: Just three weeks after the shooting in Parkland, the then-governor of Florida, Republican Rick Scott — now in the U.S. Senate — signed a bill shifting the age for purchasing a firearm from 18 to 21. But the choice of 21 was arbitrary. Recent research in neuroscience suggests that 25 makes more sense.

Of course, young people have no monopoly on the deadliest mass shootings in modern American history. The killer in Las Vegas, who murdered 58 people, was 64; the perpetrator in the Pulse Nightclub shooting in Orlando was 29; the gunman at the Tree of Life synagogue in Pittsburgh, 46. But people in their teens and early 20s are heavily represented among the worst perpetrators: The Columbine shooters, for example, were 17 and 18. The Newtown, Conn., gunman was 20. At Virginia Tech, he was 23. Aurora, 24. Charleston, 22. Parkland, 19. To that list we can now add the suspects in the Atlanta and Boulder incidents, who were both 21. (According to a database maintained by scholars at the Rockefeller Institute of Government, the average age of a mass shooter is in the low 30s.)

Several businesses whose profits depend on the safe use of their services recognize the risk posed by people in their late teens and early 20s. For decades, insurance companies have charged young drivers and their parents high fees because they are responsible for a disproportionate share of accidents. Most car-rental companies refuse to serve people under 25.

Both industries came to this conclusion after looking at actuarial tables. In 2019, for example, Americans ages 20-24 died at a higher rate than anyone under the age of 80. Sensory deficits and slower reflexes are the problem in the latter group, recklessness in the former. The analogy between driving and gun safety is not incidental. In America, car accidents are the leading cause of death in teenagers and young adults. Gun violence is second.

And 25 is an important age when it comes to mental health, as well. Seventy-five percent of people who are going to develop any psychiatric disorder, whether anxiety, depression or eating disorders, do so by age 24. And the peak age of onset of psychotic disorders in males, specifically, is, once again, just under 25.

Among the most prominent symptoms of psychotic disorders are delusions, disordered thinking and social withdrawal. Incipient versions of these symptoms usually emerge in the years leading up to a first episode, as the brain veers off the road of normal development. Among the early warning signs of nascent psychosis are a worrisome drop in grades; emergence of peculiar thoughts, paranoid ideas or inability to maintain attention; and social withdrawal.

Most people with psychiatric problems — including disorders on the schizophrenia spectrum, as well as other forms of psychosis — will never commit violence. But a small subset will, particularly around the time of their first psychotic episode, and assault weapons and psychosis are a risky combination.

About 25 percent of people showing early warning signs of psychosis have violent thoughts and fantasies; of this group, about 1 in 5 will display violent behavior in the months before or shortly after conversion to psychosis. The diaries, manifestos and videos left behind by young mass shooters often show the paranoid or delusional thinking characteristic of psychosis, as well as the violent obsessions characteristic of people who are both psychotic and dangerous.

People who knew the Parkland shooter, Nikolas Cruz, saw ominous signs for years, which intensified shortly before the emergence of his violent fantasies of “shoot[ing] up a school.” The police had to be called dozens of times, as early as age 10, to stop his violence toward animals, neighborhood kids and family members.

We do not yet have a full picture of the alleged shooters in the Boulder and Atlanta tragedies, but the evidence is suggestive of potential psychosis. Ahmad Al Aliwi Alissa, the alleged Boulder shooter, alarmed his high school friends by becoming increasingly short-tempered and violent; he quit the wrestling team in a rage, yelling “I’m going to kill you guys!” One of his brothers told a reporter that Alissa was becoming increasingly paranoid — that he thought he was being chased, or that someone was following him.

The life of Robert Long, the alleged Atlanta shooter, was also on a downward trajectory suggestive of intense mental distress: He quit college and appeared to have a tortured inner life, alternating between visiting massage parlors and consuming pornography and falling into suicidal ideation because he thought he was “walking in sin.” He told police that he killed to destroy sexual temptation: Confusing the inner world (his own desires) with the outer world (lashing out to “solve” those problems) is a clear sign of disordered thinking.

In each of these cases, impulsivity may also have combined with mental illness, with catastrophic results.

The convergence of evidence suggests that two gun safety measures might save lives and reduce the number of mass shootings. One would be a public health campaign aimed at educating parents, teachers and others about the early warning signs of psychosis in young people, including information on whom to contact if they have serious concerns about potential for violence. Another would be to adjust existing age-related gun restrictions to recognize the impulsivity and vulnerability to mental illness of people under 25.

Of course, the efficacy of these laws have their limits, given that not all guns used to kill people are obtained legally. Young people might retort that if they are old enough to serve in the military, they should be old enough to buy weapons. But federal law already prohibits the sale of handguns by licensed dealers — though not unlicensed dealers — to people under 21. Relying on science to revise that age limit by four years and applying the same limit to gun shows and private sales is hardly a stretch.

Naturally, age-based restrictions should be just one part of a broader effort to curb the epidemic of gun violence. By an 8 to 1 margin, Americans support universal background checks; for a national database of gun sales and a ban on all assault weapons, the margins are 3 to 1 and 2 to 1, respectively. But the political parties are divided on these questions. As we look for ways to find common ground on this contentious issue, the indisputable evidence that young people are particularly prone to gun violence might provide one opportunity for bipartisan action.