I can't see your photo you posted, but from what it sounds like, you may have a cockerel on your hands. (The terms "hen" and "rooster" are used for birds over a year old, for birds less than a year old, they're called "pullets" and "cockerels." Which, thank you for specifying age here, it really helped out here.)
For cockerels, usually they'll go crazy with hormones within six months to a year. Regardless of the bird's gender, I'd try and remedy that aggression as soon as you can. (There are a lot of people on here who have asked at one point "how do I remedy a mean rooster?" so if you're curious you can definitely find it on here if you search.) Aggressive behavior like that will only make you (and your hens) miserable. Also, if your bird is a rooster and starts attacking you or your hens, he may be too far gone and simply cannot be rehabilitated; in that case you'll probably have to get rid of him, for the safety of the rest of your flock. It's sad, but it is a possibility here, so please keep that in mind.
Because of this, my boys aren't allowed to have a name until they're over a year old. They earn their names when they show that they're sweethearts and aren't going to turn nasty.
But if it turns out you don't have a cockerel (or another rooster in your flock, and you have all hens), and your bird in question is indeed a pullet (ie, if she's laying, which is a pretty dead giveaway as to which gender she is
), she could just be demonstrating "roo behavior." Sometimes in an all-hen flock there will be that one hen who tries to take on the "rooster role" in the flock. She'll try to mate the hens, rule the proverbial and literal roost, and she'll even try to crow and everything, it's so weird!