A US District Court judge has declared unconstitutional federal laws banning handgun sales by licensed dealers to people under 21 years of age, saying anyone over 18 should have that right.

Judge Robert Payne of the Eastern District of Virginia issued the ruling in a case filed by four men who were over the age of 18 but under the age of 21 when they wanted to buy handguns.

Federal law prohibits licensed gun dealers from selling handguns to persons under the age of 21, although parents can buy them for their children or they can purchase them themselves in private sales or at gun shows.

While Americans under the age of 21 cannot currently purchase a handgun from a federally licensed dealer, they can buy a rifle or shotgun.

In his opinion on Wednesday, Payne cited a recent Supreme Court decision that expanded the rights of gun owners and the Second Amendment to the US Constitution, which states that "the right of the people to keep and bear arms, shall not be infringed."

"The Court finds that the right to purchase a gun falls within the Second Amendment's plain text," he said.

"No federal appellate court, much less the Supreme Court, has squarely determined that the Second Amendment's rights vest at age 21," he said.

Payne noted that the voting age in the United States is 18 and that is also the age for enlistment in the military.

The drinking age is 21 and Congress has raised the age to purchase tobacco to 21, he said.

But unlike the Second Amendment, the judge wrote, "there is no similar constitutional right to consume alcohol or to use tobacco."

Everytown Law, a gun violence prevention organization, denounced the judge's ruling.

"Not only are guns the leading cause of death for US kids and teens, but research shows us that 18- to 20-year-olds commit gun homicides at triple the rate of adults 21 years and older," Janet Carter, senior director of issues and appeals at Everytown Law, said in a statement.

"The Court's ruling will undoubtedly put lives at risk," Carter said. "It must be reversed."

The case may eventually wind up in the Supreme Court, which has swung firmly to the right since former Republican president Donald Trump named three justices.

It comes amid a spate of mass shootings in the United States and efforts by the administration of President Joe Biden to persuade Congress to ban semi-automatic rifles frequently used in the attacks.

In 2021, more than 47,000 people were killed by guns in the United States, including suicides, according to the Gun Violence Archive.