I have 9 of them. I have 2 adult males that sometimes get feisty with one another but mostly they ignore each other. I have two young ones that are almost two years old now and the other five are females. Most of those are sub-adults.

Yes, all of mine are ornates.

As far as your aggressive one I would let him have as much exposure to the others so that he gets used to being around other turtles. I have had males (and females) that get aggressive also, but turtles are very good at handling that kind of behavior. They will simply close up shop and withdrawl into their shells. The aggressive ones will learn soon enough its a waste of time and energy. In less than one week most if not all of that behavior will go away. Before long they will all be one happy family.
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Vichris
"The object of life is not to be on the side of the majority but to escape finding oneself in the ranks of the insane"- Marcus Aurelius