When the female is a year old or maybe a bit before and the roo..........????? maybe 9 months or so, and yes it is a combination of things. Something you may not want to hear, but it's an important issue, and that's about the practice of artificial insemination. From the looks of your birds, I'm going to guess that you will need to, the better the birds the more help they need. Yours appear to have plenty of fluff, so you may never have fertile eggs without help. You're going to get arguments about this and I know some people have good luck with their birds breeding naturally but trust me, it may be an issue. I have one rooster that is an excellent roo and is able to fertilize any hen that he is with, but I've got more roos that can't get the job done and need assistance.