TALLAHASSEE — A federal appeals court next month will hear arguments in the National Rifle Association’s constitutional challenge to a Florida law that prevents people under age 21 from purchasing rifles and other long guns. The 11th U.S. Circuit Court of Appeals last week scheduled an Oct. 22 hearing in Atlanta, as it considers a law that passed in the aftermath of the February 2018 mass shooting at Parkland’s Marjory Stoneman Douglas High School that killed 17 people. A federal district judge and a three-judge panel of the appeals court upheld the age restriction, but the full appeals court last year decided to take up the case in what is known as an “en banc” hearing. As the Florida lawsuit has played out, the U.S.