I don't know. You can tell early by their wing and feather color. The females have penciling feathers and the males will have more solid looking feathers. Yours looks just like mine at that age and I for sure have a female.
I agree, I have two 7-8 week old dark brahmas and out of my other 4 chickens (2 production red and 2 black australorp) the dark brahmas are the nicest! So congrats!