For some this can be sooner. We try to take the last litter before the female's first birthday. Most of our females will only have two litters. The female hamster comes into season every four days. This means that three out of the four days she will not want to know the male at all.
Some females just walk briskly out of reach, others reach for a chunk of fur.
When putting your hamsters together for the first time, be prepared to split them. A good way that we have found recently is to put an empty plastic ice cream tub or margerine carton over one of the party and whisk the other back to its cage. Then you can remove the one under the tub. When the female comes into season, it is unmistakeable. If you touch her sides, or if the male puts a paw on her back, then she will stand stock still, all four legs apart and tail slightly up.