How old should a baby guniea pig be before you put it in the same cage as another guinea pig?

Baby guinea pigs, also called pups, should not be separated from their mothers until they are three weeks old. At that point, they are old enough to live with another male or female guinea pig. Male and female guinea pigs can be kept together regardless of their ages, but two males should not be kept in the same cage unless they have been neutered. If not, they will likely fight.