personally i wouldnt try to incubate eggs from young hens that have just started laying i would wait a couple of months, the eggs will get larger and better developed as the hen matures more plus you get to know them better, some will lay 'better' eggs than others and you can start learning what to look for yourself .. if you want to try it early theres really no reason not to but i wouldnt be expecting a serious result with the first few eggs out of fresh young hens .. but if you got a good rooster doing his thing theyre going to be fertile lol, again i wouldnt rush it ..a young rooster assuming he's the same age as the hens doesnt have his act together great either for a couple more months after theyre laying ..