Guinea pigs are unlike other small mammals in the area of reproduction. Most small mammals can be bred at any time during their life without many complications. In the guinea pig, also known as the cavy, this is not always the case. Guinea pigs, males and females, reach puberty around 3 to 4 months of age. At this point, it is time to breed your female for the first time. This may seem a little young but guinea pigs bred after 7 months of age for the first time can have significant health problems.
To learn more, read Guinea Pig Dystocia and Pregnancy Toxemia