Hmmmmm why do hatchery chicks start later?[/quote]
Some hatchery chicks start earlier. Some hatchery chicks start later. Some non-hatchery chick start earlier. Some non-hatchery chicks start later. How they are fed can certainly make a difference. Another big factor is heredity. Breed also plays a apart. Time of year has an effect.
Personally I don't want a pullet starting to lay real early. I prefer her body to mature more so she is better able to handle egg laying. After the first month I don't feed them a real high protein diet. That will slow their body growth and bring that more in line with skeleton growth and internal organ maturity. I generally don't select the ones that start really early for my breeders. I've got them to where most start in the early 20 weeks area instead of some in the teens.
It's a personal preference. I just don't get excited about weird eggs like yolkless eggs, soft shelled eggs, or double yolkers. And I have a mixed age flock. I always have some pullets or hens laying so I don't need the weird pullet eggs.