A federal lawsuit challenging Minnesota's age limit for permits to carry handguns in public is attracting intervention from national gun safety advocacy groups ahead of a key court hearing next month in St. Paul.

Three Minnesota residents under the age of 21, with the backing of three gun rights organizations, sued Commissioner John Harrington and their respective county sheriffs last year over the enforcement of a state law barring anyone younger than 21 from obtaining a permit to carry. More than one year — and hundreds of pages of legal arguments — later, both parties agree that they will not be able to settle this conflict on their own.

"They can vote, enter contracts and get married. They can join the military—in fact, they can be conscripted—to fight and die for their country. And as adults, there are no parents or other legal guardians generally responsible for their care and protection," wrote David Thompson, a Washington, D.C.-based attorney representing the plaintiffs, in a recent memo to the court. "Yet, the Minnesota law challenged in this case … categorically bars them from carrying a handgun in public for self-defense as other adult Americans have the undisputed right to do."

Those suing over what they're labeling as Minnesota's Carry Ban argue that Minnesota's age limit for the permits violates the Second Amendment rights of 18- to 20-year-old adults.

Minnesota's attorneys, meanwhile, counter that the state is justified in creating such a restriction. They point to data suggesting those in that age group pose a higher risk of violence with firearms, while other arguments cite high-profile mass shootings involving gunmen in that age range.

Both sides agreed to scrap a hearing designed to discuss settlement options that was scheduled for last week, telling a federal magistrate judge that they would be unable to resolve this issue. Assistant Attorney General Amanda Prutzman, representing Harrington in the lawsuit, wrote in a July 20 letter to the court that the case "presents largely legal issues regarding the scope of the Second Amendment that are very likely to be resolved in their entirety on cross motions for summary judgment" and that no settlement would be reached in which Harrington and the sheriffs would agree that the law is unconstitutional and unenforceable.

The three young Minnesota adults suing the state include Kristin Worth, a woman who works at a bank in Milaca and wants to carry a firearm for self defense. She told the court that she was repeatedly harassed last winter by two "significantly larger" men and required an escort to her car.

Another plaintiff, Austin Dye, a man from Washington County, cited "a rise in civil unrest and some types of crime both in Washington County, as well as in St. Paul where he visits his stepfather" for wanting to carry a handgun for self-defense. Axel Anderson, of Douglas County, also is among the plaintiffs.

They are joined in their suit by the Minnesota Gun Owners Caucus, the Second Amendment Foundation and Firearms Policy Coalition. They are suing Harrington, Mille Lacs County Sheriff Don Lorge, Douglas County Sheriff Troy Wolbersen and Washington County Sheriff Dan Starry.

U.S. District Judge Katherine Menendez is scheduled to hear arguments for summary judgment in the case Oct. 4 in St. Paul.

Harrington, in court filings, says the plaintiffs are mischaracterizing the state's policy as a "carry ban" — pointing out that the law only bars adults younger than 21 from carrying a firearm in a public place.

"In Minnesota, 18-to-20-year-olds have the right to own and bear arms in their homes, on their land and in their places of business," Prutzman wrote in a legal memo last month. She also noted that they may carry firearms between homes and workplaces without a permit and that they may likewise do so for target shooting or hunting.

Prutzman added that the new Supreme Court ruling did not establish 18- to 20-year-olds as part of "the People" to which the Second Amendment applies. Historically, she added, those in that age group were legally minors when the Second and Fourteenth Amendments were adopted. She also argued that laws governing militias underscored that those younger than 21 did not have independent rights to carry firearms and that many laws required guardians or parents to procure them.

Last month, several national and state-based gun safety groups joined the case to support Minnesota's age limit on permits: the Michael Bloomberg-backed Everytown for Gun Safety group and a coalition between the Giffords Law Center to Prevent Gun Violence and Protect Minnesota filed friend-of-the-court briefs last month in support of the state law.

Everytown urged the judge to consider the "wealth of restrictions" on keeping and bearing arms among adults younger than 21 that dated from the second half of the 19th century.

Daniel Adkins, a St. Paul attorney filing on behalf of the Giffords and Protect Minnesota groups, cited age restrictions on alcohol and cigarettes and pointed out that the brains of those 18 to 20 years old are still developing.

He also cited mass shootings this year by 18-to-20-year-olds in Buffalo, N.Y., and Uvalde, Texas, as "a tragic demonstration of the wisdom of Minnesota's decision to regulate gun possession and use for this age group more than for older adults."

Arguments in the case also have since been shaped by the recent U.S. Supreme Court ruling that New York's requirement for a license to carry concealed firearms in public was unconstitutional. Citing that June decision, Thompson argued that Minnesota must justify its age limit by "demonstrating that it is consistent with the nation's historical tradition of firearm regulation."

"The Supreme Court was clear: The burden is on the government to prove that the Carry Ban is constitutional, and the only acceptable standard against which to judge its constitutionality is the history of traditional firearm regulation in this country," wrote Thompson.

There is no evidence of any laws restricting carry rights to 18-to-20-year-olds because of their age, Thompson contended. Instead, he wrote, the Founders "required them to possess firearms in good working order and to know how to use them so that they could be ready to serve as members of the militia if the need arose."

Minnesota's handgun carry permit law

A permit to carry constitutes a permit to purchase a handgun.

There is no law stipulating that the handgun be concealed.

Permits are valid for five years.

Applicants must show evidence of training in safe use of handgun.

Must be 21 to buy a handgun or handgun ammunition

Must be 18 to buy a semi-automatic assault rifle.

Must not have been convicted of a violent crime unless civil rights have been restored

Must not be an unlawful user of any controlled substance.

Must not have been committed to a treatment facility as chemically dependent unless you have finished treatment or civil rights have been restored.

Must not have been judicially committed to a treatment facility in Minnesota or elsewhere as "mentally ill," "developmentally disabled" or "mentally defective," or "mentally ill and dangerous to the public."

Must not be illegally or unlawfully in the United States.

Must not have been discharged from the armed forces of the United States under dishonorable conditions.