From The Washington Post:

A panel of the U.S. Court of Appeals for the 4th Circuit dissolved its ruling because the Virginia woman who initially brought the lawsuit turned 21 before the decision became official.

The challenge to the age restrictions was brought by prospective handgun buyer Natalia Marshall, who was unable to purchase a handgun from a federally licensed firearms dealer in Virginia because of her age. Once Marshall turned 21, she was no longer prohibited from buying a handgun, and there was no longer a legal controversy, the court said.