"You're under-age!" Mrs Weasley shouted at here daughter as Harry approached. "I won't permit it! The boys, yes, but you, you've got to go home!"
Ginny's hair flew as she pulled her arm out of her mother's grip.
"I'm in Dumbledore's Army -"
"- a teenagers' gang!" [I supposed it's been said by George]
"A teenagers' gang that's about to take him on, which no one else has dared to do!" said Fred.
"She's sixteen!" shouted Mrs Weasley. "She's not old enough! What you two were thinking, bringing her with you -"
Harry Potter and the Deathly Hallows
In this scene, Mrs Weasley didn't permit Ginny to fight against Voldemort. I don't understand what Fred was saying: "A teenagers' gang that's about to take him on, which no one else has dared to do!". Is 'him' referring to Voldemort? But Voldemort has not been mentioned in the near context.