Good question. I'd like to know, too. I wonder how one would go about finding out. From the looks of them when cracked open, with their flat yolks and no structure to the whites, they must be pretty old.
Well, since you can almost always peel them when hard boiled, they have to be at least a week or 10 days old. And I read somewhere that by law commercial eggs have to be shipped by the time they're 30 days old. Not sold, mind you, but shipped!!
Don't know if this is still current law, or if it applies to all states, but it's what I've read.
Look on the side of the egg carton for the date. Some will have the actual date and some will be the Julien date. 001 is the 1st day of the year and would be Jan 1st and a Julien date of 045 would be the 45th day of the year which would be Feb 14th...etc etc...
I guess on average about 2 to 3 weeks old.
Now this is an interesting question. Next time I'm in a store, I'll have to check for dates.
I would guess like Rte.66_chicks said, the quality is poor compared to "our" own grade A eggs. Anemic, sagging, watery eggs. I would think that they would be 10 plus days with how they are broke down. (super question and of course I give an uneducated guess!)
If you have any that last that long, check out your own eggs at a month. They will be firmer than any storebought egg that has a julian date showing it to be a month. It's not just the age, it's what the poor chickens are fed and how they live that makes their eggs so substandard.
Also, the date on the carton is the date of packaging, not the date of laying. Someone correct me if I'm wrong, but I think the regulation is that eggs have to be sold within 45 days from packaging, but that there are no restrictions about how long they can sit around before packaging.
All that said, eggs are expensive to store in warehouses, so I suspect that the eggs are packaged pretty quickly. It doesn't mean that they aren't at least a couple of weeks old by the time they reach our store shelves, though.