Nearly six years after a 19-year-old fatally shot 17 people at Marjory Stoneman Douglas High School, Florida Republicans are pushing to lower the legal age for buying rifles and other long guns back to 18.

Lawmakers in 2018 raised the purchase age to 21 following revelations that Stoneman Douglas shooter Nikolas Cruz had legally purchased the AR-15-style weapon he used in the attack.

Tony Montalto, whose 14-year-old daughter Gina was killed in the shooting, testified against lowering the age. “Our current law is working,” he said during a Jan. 30 Criminal Justice Subcommittee hearing in Tallahassee. “I implore each of you to remember that law is written in the blood of the victims, including my beautiful daughter, Gina.”

Jayden D’Onofrio, 19, also spoke against the bill, recalling that he was in middle school nearby when Cruz attacked the high school. “Consider the facts,” D’Onofrio said, “18-to-20-year-olds are three times more likely to commit gun homicides.”

Several speakers repeated D’Onofrio’s claim before the subcommittee advanced HB 1223 along party lines, with Republicans in favor and Democrats opposed. (It has one more committee before it can be heard on the House floor.)

We wondered: Does data show the age cohort having that high of a propensity to fatally use firearms against others? And if so, why?

Data shows younger Americans are likelier to commit fatal shootings

Crime data in the United States is notoriously incomplete, but experts agreed that general trends from state and FBI data show people ages 18 to 20 — and in many datasets people in their early-to-mid 20s — are likelier to commit deadly shootings than other age groups.

Gun control advocacy group Everytown for Gun Safety said in a June fact sheet that “data show that 18-to-20-year-olds commit gun homicides at triple the rate of adults 21 and older.”

The group’s media office said researchers arrived at that calculation using the FBI’s supplementary homicide report and the U.S. Census American Community Survey from 2016 to 2020. Everytown’s researchers said they considered variables in the FBI data, including crime type, weapon and offender’s age. Researchers then used census population data to estimate each age group’s rates of committing a fatal shooting. (In most datasets, “firearms” includes both long guns and handguns.)

Federal law requires people to be 21 to buy handguns, but some states permit buying long guns as young as 18. Florida’s law, and the proposed bill, is centered on long guns, which include rifles, carbines, shotguns and submachine guns. The AR-15 semi-automatic rifle falls under this category.

After an 18-year-old shot and killed 21 people at Robb Elementary School in Uvalde, Texas, in May 2022, Cassandra Crifasi, research and policy director at the Johns Hopkins Center for Gun Violence Solutions, discussed how much likelier people in that age group are to commit violent acts.

“We know that 18-to-20-year-olds have some of the highest risk for gun homicide perpetration, so this is a risky group when they have firearms,” Crifasi said. “But very few states have done anything to address gun access among this age group.”

Jeff Asher, a data analyst with expertise in evaluating criminal justice data, looked at data from Florida Department of Law Enforcement’s Supplementary Homicide Report. The report’s 2020 figures (the most recent year with complete data) showed that 18-to-20-year-olds were identified as perpetrators in fatal shootings at “three times the rate of 16-year-olds” and about “three times the rate of a person in their 30s,” he said. They were the offenders at nearly twice the rate of people in their 20s, Asher found.

Daniel Webster, distinguished research scholar at the Johns Hopkins Center for Gun Violence Solutions, told PolitiFact that FBI data on murders and nonnegligent manslaughters that he has studied over the years show 18 as the peak age for homicide offenders, followed closely by 19 and 20. In 2021, about 81% of homicides involved firearms, according to Pew Research Center.

“It’s not a direct measure, precisely, but it’s a pretty darn good proxy,” Webster said.

James Alan Fox, a Northeastern University criminology professor who has maintained a database on U.S. homicides dating back to 1976, said he’s found that the rate of gun homicides starts to increase around age 14, and peaks around age 20.

Fox looked at homicide data from 2016 to 2020 and found that 18-to-20-year-olds comprise 4% of the U.S. population, but commit 17% of gun homicides and 16% of gun homicides by rifle.

“Gun homicides are particularly youth-dominated,” Fox said. “I would like to see the age (for purchasing firearms) be 25, which would be consistent with the data and what we know about brain development. At least, it should be the same as handguns, which is 21.”

Brain development, societal factors may be behind the spike, experts say

The human brain doesn’t finish developing until people are in their mid-to-late 20s. The prefrontal cortex, the brain region responsible for executive control, including skills such as planning, prioritizing and making well-reasoned decisions, is one of the last parts to mature.

Criminologists, gun researchers and health policy experts have long said that this lack of development is a primary driver of impulsive behavior among young people. Laws that raised the legal drinking age for alcohol to 21, they said, arose out of data that showed there was inherent riskiness in allowing 18-, 19- and 20-year-olds easy access to alcohol.

“People that age can be impulsive, impatient and imprudent, and will often make actions without fully thinking about the consequences for themselves, much less their victims,” Fox said.

The time period is key. The structure of high school is gone, Webster said, presenting a transitional period in which many people in this age group can act in dangerous, impulsive ways. It’s also cultural, he said, as the vast majority of gun homicides are committed by young men who are often trying to demonstrate that they aren’t weak, and are willing to be violent.

“You’ve got cultural reasons, you’ve got biological reasons, you’ve got changing social positions,” Webster said. “All of this makes this group far more vulnerable to doing really dangerous things.”

PolitiFact copy chief Matthew Crowley contributed to this report.

This fact check was originally published by PolitiFact, which is part of the Poynter Institute. See the sources for this fact check here.