My understanding is that as long as storage conditions are per manufacturer's recommendation, rods should last almost forever.
Sometimes humidity gets into packages which can affect how well rods run; possibly because of water chemically changing the coating? or rust building to intolerable levels but that is for non- low hydrogen rods. Usually you will know it by how the rods run. If you know what to look for and they aren't acting right, I would try fresh rods but would have no concerns otherwise.
Low hydrogen is supposed to be stored in hermetically sealed packages or in rod ovens. When they have been in the oven for a long time, you might notice the flux breaks off more easily but they should still give sound welds (that is for the rods where the flux stays on, of course.)

Having said all that, I need to leave you with this: If you have any doubts at all, you might find that replacing old rods with new is cheap insurance. You can't afford to replace a limb or a life.
CHGuilford