According to a Reuters report on the 5th Circuit's decision:
The 5th U.S. Circuit Court of Appeals in Houston rejected the NRA's argument that 18- to 20-year-olds had a right to buy the guns under the Second Amendment to the U.S. Constitution, as well as the equal protection clause of the Fifth Amendment.You may remember that the Brady Campaign and other gun prohibitionist played gutter politics with this case. They accused James D'Cruz, then a freshman at Texas Tech, of having a Facebook page filled with "angry, violent Facebook postings." D'Cruz was further demonized by Josh Horwitz of CSGV who said "he's a poster boy for why we should prevent handgun sales to those under 21 years of age" and implied that he sounded like a school shooter.
A unanimous three-judge panel said Congress, in a law dating from 1968, adopted the sales ban to help curb violent crime. It also said that the nation's founders and 19th-century courts and commentators believed that disarming specific groups did not trample on the right to bear arms.
"Congress was focused on a particular problem: young persons under 21, who are immature and prone to violence, easily accessing handguns," mainly from licensed dealers, Judge Edward Prado wrote for the panel.
"The present ban appears consistent with a longstanding tradition of age- and safety-based restrictions on the ability to access arms," he added.
The full 41 page opinion of the 5th Circuit can be found here. I have not had time to read it but hope to have an update posted after I have done so.