When is an egg too old to set?

I've held and hatched eggs up to 4ish weeks old. I think as long as they are stored correctly and turned a couple times a day, they will be fine. But, I've read that hatchability will go down after 7-10 days.

 

When I was actively hatching chicks, I incubated eggs that were up to 3 weeeks old with good hatchability. These were not shipped eggs.

 

I suggest you read this. It talks quite a bit about storing eggs for incubation.

Texas A&M Incubation site
http://gallus.tamu.edu/library/extpublications/b6092.pdf

The way I look at recommendations on this site, almost everything is a guideline, not a hard and fast law of nature. Many of us violate some of these recommendations all the time and do OK. I usually store my eggs in temperatures warmer that these guidelines suggest and do OK. Maybe my hatch rate would go up a bit if I had a cooler place to store them, but I don't have that place so I don't worry about it too much. The intention of the recommendations is to improve your odds of something good happening and reduce your odds of something bad happening. If you follow the suggestions exactly, there is no guarantee that you will have a great hatch. If you violate a few, there is no guarantee that you will have a lousy hatch. If you follow what you can, you have probaly improved your odds that something good will happen. So I suggest don't overobsess about these but do what you reasonably can.

Good luck!