Hi, my chicks are a month old and I will be integrating them into the coop with two hens before summer is over. (They are stil in a large brooder as I have no seperate enclosure for babies, just my older hens' coop). 1). At what age can they eat the lay mash the hens eat? They currently are still on medicated mash. 2). Also, they pick through the grit pan I have for the hens; is this okay? There is a bit of oyster shell in the grit mix.