My vote is for hen too. At that age most boys have started to crow. Also I don't see any pointy feathers on the saddle area (though the angle of view isn't great). If it were a boy I'd expect to see at least a hint of that. No guesses on the breed but the white earlobe suggests that she may be a white egg layer.
Our "guy" got really randy by 5 months, too. I didn't order any roosters, but the hatchery let one slip in as they sexed my birds. I'll cut them some slack since they sex thousands of birds a day. We have some hens that have very pronounced comb and wattle, but they are not roos. It confused us at first, but just like humans, even within the same breed (buff Orpingtons) there can be some genetic variation. So, we started to watch individual and flock behavior and that helped us confirm that all our other birds are hens.
Our rooster developed very pronounced comb and wattles, yes. But, it was his neck feathers, amorous behavior and early crowing that was certainly in place by 5 months which removed all doubt. And when I write "amorous behavior" I mean he hops on every hen he can capture by the neck with his beak.
As far as the breed, my guess would be Easter Egger mix because of the slate legs and the black feathers in the neck area are like a washed out version of my Easter Eggers. Mine all have pea combs though so this ones probably mixed with a brown/white egg layer...I guess you'll find out when she starts laying!