Egg freshness--stale eggs at market?
Individual eggs may have large air cells and still be fresh, but in general large air cells equate to old eggs, and possibly eggs that were stored at too high of temperatures.  At higher temps, the air cell grows faster.

To test, use a small flashlight and shine it through the egg, and you can find the outline of the air cell.  It is a bit more difficult with colored eggs, and you may have to use shadows to see the air cell in bright conditions.

For the record, eggs are often stored incorrectly.  Properly stored eggs should be placed with the air cell up, not down.  The rounder side of the egg should have the air cell, the more pointed side should be placed down.  The reason is, the air cell breaths through the porous shell as nature designed.  Putting the air cell down, slows this breathing.  Not only does this slow the growth of the air cell, sometimes making the egg look fresher than it really is, it also increases the chance of the egg trapping gases and going bad.  Stored flat is also fine as again, the egg can breath, it is in cartons and such that orientation matters, and for some reason many believe the pointed side goes up and that seems to me the more common orientation when put in randomly.