I don't know about feed as mine free-range for the vast majority of their food and get wheat and corn otherwise. 3 of my hens have started laying and they have all done the same thing, for days and days before the first egg they look around for a suitable place and you may find them poking around the nest boxes. When they get really close they start making a fuss a lot, wandering around anxiously and may do the egg song even if they haven't laid yet. Your girls looks of age to me, you can put fake eggs in their nest boxes to clue them in as to the proper location. I'd also look around for other nests too.