I have 3 groups of chickens, they are divided by age. One is 1+ years old and is eating layer pellets, one group is 6 weeks old and eating starter/grower crumbles, and one group that is 3 1/2 weeks old and also eating starter/grower crumbles. How young can I start my young birds on layer feed? Or can I feed my adults starter/grower (as long as I use oyster shells for them) so I can get all 3 groups on the same feed by the first of September. I am hoping to have all 3 groups intergraded by the middle of September at the latest. I am going on vacation for a month and want to keep things simple for my chicken sitter.