Over the years I have noticed that eggs not shipped at home an set in the incubator from 1-7 days old,hatch very well with normal chicks and good hatches.After 10 days the hatch rate starts dropping,but still good up to 14 days.Older eggs sometimes will hatch,but the chicks are often weaker and the hatch rate very low.The eggs need to be turned and keep at a steady temperature,at appox. 50 degrees with high humidity.They membranes will stick if not turned and the egg drys out over time in low humidity.Extra large and jumbo sized eggs seem to not hatch as well as medium and large,but it is not dramatic. For shipping 1-4 days is fresh provided they can be delivered within 3 days,you can always include a few free extras that are a day to two older.