In most states, an American can buy an AR-15 style semi-automatic rifle after their 18th birthday.

Law enforcement officials say that’s what happened about a month ago in Texas, when Salvador Ramos purchased AR-15-style rifles and ammunition from federally licensed firearms dealers just days after he turned 18. On May 24, he used those weapons to kill 19 students and two teachers at Uvalde’s Robb Elementary School. 

In more than 40 other states, it is possible for someone as young as Ramos to purchase an AR-15. 

Mass shooters younger than 21 used AR-15-style rifles for attacks in Newtown, Connecticut, in 2012; Parkland, Florida, in 2018; and Buffalo, New York, in May 2022. A National Institute of Justice study found that 77% of people who commit mass shootings "purchased at least some of their guns legally." 

At the same time, the age limit to buy handguns in many states and at the federal level is higher, at 21 years old. 

The bipartisan gun legislation that President Joe Biden signed into law June 25 did not raise the minimum age for buying semi-automatic rifles. But it increased scrutiny for gun buyers under 21 during background checks, requiring a review of whether the buyer has a juvenile record that would disqualify them from buying a gun. It gives authorities 10 business days to examine state juvenile justice and mental health records.

So why does federal law require you to be 21 to purchase a handgun, but not a long gun like an AR-15?

Experts say that’s because handguns are the most common firearms used in crimes involving guns. Rifles and other long guns are more associated with hunting.

"Historically, rifles and shotguns have not been subject to the kind of strict regulations that handguns, large knives and brass knuckles have been," said Brennan Gardner Rivas, a historian and researcher of Texas firearm regulations. "All of those smaller, concealable deadly weapons almost universally ... were targeted with penal statutes."

John Deloca, owner of Seneca Sporting Range, prepares to load bullets in his 9mm semi-automatic handgun for a shooting demonstration at his gun range on June 23, 2022, in New York. (AP)

Most of the gun laws in question were enacted in the 1960s, before weapons like AR-15s became "a mainstay of gun culture," said Ari Freilich, the state policy director for the Giffords Law Center, a gun control advocacy group.

Here’s an overview of federal laws setting age requirements for gun purchases and how they collide with state policies that vary across the country.

Federal law regulates handgun sales differently than sales of shotguns and rifles, including AR-15-style rifles. (Over the years, "AR-15" has become an umbrella term that is colloquially used for a variety of semi-automatic rifles.) 

Under federal regulations, it is unlawful for licensed firearms importers, manufacturers, dealers and collectors to sell firearms or ammunition to someone who is younger than 18.

The law goes a step further in regulating handguns. It says if the licensed dealer wants to sell or deliver firearms "other than" a shotgun or rifle, or ammunition for those weapons, then the buyer must be at least 21 years old.

Simply put, this means that licensed dealers cannot sell handguns to people under 21 and cannot sell long guns, including AR-15s, to people under 18.

An AR-15 style rifle manufactured by Battle Rifle Co. is displayed in Webster, Texas on March 15, 2017. (AP)

Anyone repetitively buying and selling firearms for profit must be licensed by the federal Bureau of Alcohol, Tobacco, Firearms and Explosives. Along with the minimum age restrictions, licensed dealers must meet other standards, such as maintaining records of their sales and conducting background checks on a person buying a gun. 

Not everyone who sells guns has a federal firearms license. A person who inherited a collection of firearms and decides to sell the weapons, for example, is not required to be licensed. And experts say that some people who should be licensed are not. 

"It has been well documented that there are many people who do repeatedly sell guns for profit that should have a license under this standard, but don’t — often folks who sell a lot of guns online," Freilich said. 

There was a ban on the sale of a variety of assault weapons, including some AR-15-style weapons, from 1994 to 2004. But when that law expired, semiautomatic rifles such as AR-15s were "treated just the same as bolt-action hunting rifles," meaning licensed dealers under federal law are permitted to sell them to people age 18 or older, Freilich said. 

States can set higher minimum age restrictions for firearm sales, and some have.

Following the recent deadly mass shootings at a supermarket in Buffalo, a medical center in Tulsa, Oklahoma, and Robb Elementary School in Uvalde, lawmakers in Rhode Island raised the legal age to purchase firearms to 21.

New York Gov. Kathy Hochul, a Democrat, also signed a law June 6 requiring people to obtain a license before they can buy semi-automatic rifles. To obtain a license, people must be at least 21 years old.  

Florida, under Republican leadership, raised the minimum age for all firearms purchases to 21 just weeks after a gunman shot and killed 14 students and three faculty members at Marjory Stoneman Douglas High School in Parkland on Feb. 14, 2018.

In total, eight states — California, Florida, Hawaii, Illinois, New York, Rhode Island, Vermont and Washington — have increased the minimum age a person can purchase a long gun to 21, according to Giffords Law Center to Prevent Gun Violence data.

Magaly Newcomb, right, comforts her daughter Haley Newcomb, 14, a student at Marjory Stoneman Douglas High School, at a memorial outside the school in Parkland, Florida, on Feb. 18, 2018. (AP)

In contrast, some states have laws on the books that set the minimum age restriction for purchasing a handgun at 18 — rather than the federal minimum age of 21, when buying from a licensed dealer.

If a licensed gun dealer sold a handgun to a 19 year old — a violation of federal law — in a state where the minimum age to purchase a handgun is 18, prosecutors such as U.S. attorneys or the FBI could prosecute that violation in federal court. 

"The state can’t prevent application of the federal law, and so in order to comply with the federal law, you’d have to comply with the stricter version," Freilich said.

Sixteen states also require firearms dealers to get a state-issued dealer license, which can come with specific restrictions, according to Giffords Law Center to Prevent Gun Violence data.

In addition to age restrictions, federal law prohibits certain people from possessing firearms or ammunition, including people who have been convicted of felonies or those who are subject to an active court order that prevents them from stalking or harassing an intimate partner. 

"The reality is, if you’re a member of a prohibited category, you lawfully cannot buy a gun from anyone," said Jaclyn Schildkraut, interim executive director of the Regional Gun Violence Research Consortium. But, in practice, if you’re not purchasing a gun from a federally licensed dealer, "it is far more gray."

An unlicensed seller is not required to run a background check to determine whether a buyer is a member of a prohibited category, she said. 

"These unlicensed sellers are generally restricted from selling or delivering handguns to people under 18," Freilich said. "And there are no federal … minimum age restrictions on unlicensed people selling and delivering rifles or shotguns to people under 18."

For buyers who believe or know they would fail a background check, he said, these unlicensed sellers are an attractive source of weapons.

"Essentially, it’s like walking into an airport and you have the choice between going through a security line and just walking on the plane," Freilich said.