I have a big 2lb male that gets into scuffles every now and then. He looks like a roof rat.. or a New York rat. Huge boy!

When he starts getting all huffy, I put everyone into the bathtub and bathe them. The cage gets a full scrub down too so nothing smells like "BOY".

You can put vanilla on them, or embarrass the crap out of them(bathing)

Some rats do develop pituitary tumors that affect their behavior and temperment, and that may be something to think about.

Usually though, males just get crotchety when they get older, especially if they aren't neutered. If it continues, I would just separate them.

And I REALLY wouldn't put the unneutered boy in with the girls, regardless of how old they are. Sometimes they can have heat cycles, even if they are erratic, and they can get pregnant(like women going through menopause). I know I wouldn't want a 2 year old girl getting pregnant, it can cause alot of problems.