At 13 weeks it's new feathers often called a 'juvenile molt'. Even adult birds in molt will look like that during annual molt sometimes. Molt can be hard, with bare spots and they look horrible, or it can be soft and barely noticeable unless you really look. It can vary from year to year and from bird to bird.
https://www.wideopenpets.com/everything-you-need-to-know-about-molting-chickens/
https://www.wideopenpets.com/everything-you-need-to-know-about-molting-chickens/