Hi Eric, First, its not useful to use ages, as age has little meaning with reptiles. I could have a one month old Cross that 20 inches and your 4 month old could be 12 inches. See what I mean. With reptiles, size is the meaningful measurement, not age.
Also, if you have a sexual pair, members of the gouldi complex rarely fight. But indeed, if they are raised together, they can perform better.
Also, about raising them together. If its to insure opposite sexs, I am not sure that is a good reason, unless they were raised from day one. If one dies because you do not know how to raise them, then what sex they are, has little meaning. If its about learning to get along with other monitors, then its a very good idea.
All decisions of this nature, are more based on your abilities and experience. If you are a beginer, you may be better off keeping them seperate. Then deal with the problems, if and when they occur at a later time. You will have more experience then. If you are experienced with successful rearing of monitors, then raising them in groups should not be a problem.
I do not know if your a beginer or not, but a common problem with beginers is, they aim at the wrong goal. They are concerned with getting aduld sexual pairs, when they should be concerned with the successful raising of the baby monitors they have.
My advice is, take one step at a time, become successful at your first step, then each following step, and you will not have so many problems. Good luck F