Hamster become sexually mature as early as 4-5 weeks old but this is way too young to start breeding and can lead to complications. The best age to breed a female is from 4 months old. A female syrian will go into heat every four days. This fourth day is the day when you should attempt to mate. When the time is right place the female in the males cage or create a neutral area for them to mate. Never place the male into the females cage.