4 months sound more like it. I can't say if its a boy or girl, im no expert. However, are you sure its an australorp? The feathers don't look very fluffy, which I think they should be. My australorp looks significantly fluffier. Yours look more like my black sex-link. When you hold the body, is the feathers tight against the body, or is there lots of fluff?
his feathers were probably down because i had to catch it (very hard runs all over) and when i did he kinda lowered his body. but ill try to get it. a lot of black australorp pictures online look like mine. im not exactly sure how fluffy it should be but it's feathers puff out like around 0.5in-1 in out. may i ask what type of austrlorp yourr chickens are? what color are your chickens too?
Mine are black australorps. I don't have a picture right now. The most striking thing about it is the eyes are completely black. Yours look like a black center surrounded by lighter color? The feathers are fluffier looking than your pictures. They are also more "neat" ? Its like while its fluffy, the outside layer is quite smooth.
However, my australorp IS a hatchery bird, so who knows if it accurately represents the breed.
I'm having trouble seeing the comb clearly. Is it a typical single comb? Looks kind of thick. Also, the feathers do not look inky black, but that could just be the pics. Not sure of the breed. Don't see any sign of saddle feathers, so at this age, I think more likely a pullet.
Here is my hatchery Black Australorp at about 4 months.