I know I have made a very similar topic to this, but I'm still not that clear on it.
I've gotten both of my male turtles, Timmy(7 inch) and Danny(5 inch), about over 5 years ago when they were just babies. They have been living with each other throughout the years. They started to flutter at each other for some time now. (I have mistaken it for "mating" from previous books I have read before I stumbled upon this site and learned it is aggression) Soon Timmy started to bite Danny and getting help from this site, I learned that it was needed to separate them.
The two turtles swim around each other and try to do each other and show their thingys...

. Is it possible for them to mistaken each other as their opposite gender? From books and sources that I have read, their behavior is recognized as mating rituals and courtship. Recently I just got a bigger tank(it's still not the full size they need, but it was the biggest my parents would give me

), and so I thought it'd solve the problem by putting them together again, but nothing changed, they still flutter and Timmy still bites. So I separated them again. I am still confident that it is aggression and not mating since they're both males, but er..is trying to "do" each other part of the aggression and why do they show their thingys if it's not trying to impress a female but instead fighting? o_o
And also I have heard that putting a female turtle in will distract the males from each other. I do have a female turtle, but the two males totally ignore her.