My girls have been laying consistently for a few months now but I'm still seeing a wide variation in egg size day to day. Recently one has started laying single yolkers that are still real whoppers. When do the settle in to an egg size and mostly lay that size?
Each chicken will settle into their own personal sized eggs anywhere between 2-4 months of laying. Sometimes longer. Their "max" size is usually in the second year of laying, so probably about 18-24 months old. Reason store eggs are so uniform is anything "odd" is taken out. They are all graded and others go to liquid eggs and egg products.