My male Mouse when I put the male babies in there he attacked 2 of them and killed them. Most adults males will NOT like other males.
As far as I know, gerbils are fairly good with younger ones. They won't see them as a threat. Ashley (Chibi_star) put one male baby with her male, and another female baby with the mother. Unfortunatly, female gerbils are evil (lol ), and once the baby matured she killed it The male didn't kill the baby male though...it died on it's own..

I wonder why your mouse doesn't like other ones? Mice are very social creatures He could be like Frisco though...I kept Frisco alone for a couple months, and when I got Icarus Frisco decided he liked his new life as a loner