I've had an Orpington pullet with whacky, longer tail feathers that looked rooster-ish, though she did not have long, skinny, pointed saddle or hackle feathers so I knew she was a girl. She was the one that crowed every morning as a pullet, though she stopped when she began to lay. She's never crowed again. Hormones?
Australorps are an early maturing breed and can start to lay as early as 18 weeks old. I would expect a cockerel to be showing rooster specific hackle and saddle feathers at 21 weeks, especially if pullets can start laying from 18 weeks.