I am not sure, but when I hold onto my eggs for a week, they are still a lot harder to peel than store bought, which would leave me to believe that the stores are easily over a week old.
That probably doesn't help you much.
Have you tried to float the eggs? The more they float the older they are.
I hear it can be easily 3-4 weeks from laying to your fridge. However, this may not always be the case, as it has been shown that if you buy "specialty fertile eggs" they can still be hatched. This indicates to me that hen to table in some types of eggs, must be less than 2 weeks, even though I have hatched chicks out of eggs a month old. Just very low hatch rates.