"Given the early ages at which some males and females are sexually mature (females have reportedly been impregnated by 24 day old males), it is advised to remove the male young by 3 weeks at the latest. The earliest dates of sexual maturity are reported by V.C.G. Richardson in the 2000 edition of "
Diseases of Domestic Guinea Pigs" on page 15:
- Sexual maturity (female): 4-6 weeks
- Sexual maturity (male): 3-5 weeks
While not all males may be fertile this early, the safest action is to
separate the males from females by 3 weeks of age."
Source:
Guinea Lynx
Here's a guide on when to seperate the piglets.