aggresive behavior

Question
I have four RES and one of them is bigger than the other three and i found him biting the other ones, so I have had him in a separate cage for about six months.  I am wondering whether he will ever grow out of his aggresive habits, so that I can put all four of the turtles together in a bigger tank instead of having to buy two tanks.  Can you please help me out?  Thank you

Answer
Jake,

The new tank would have to be really big in order for 4 turtles to live together happily.  

Here is my answer to a similar question I've answered:

http://en.allexperts.com/q/Turtles-3543/2008/8/pet-terrapin.htm

When I put my two mud turtles together, it was in a kiddie pool that I'd converted to an indoor pond... to give you an idea of the size.

If you want to use fish tanks (I'm assuming that's the kind of tanks you are referring to), I think you'll need to keep using two.  I wouldn't necessarily say he has aggressive habits, he probably just needs his own space, like all animals do when they get older (even people).