If their stored in a decently dry, not to hot or cold place they should be good. My oldest primers are 16 years old, cci small rifle magnum, ive only got about 900 left of the original box of 1000, heh.
My Father stopped reloading pistol ammo some time around 1980. He kept stuff in a basement (dry floors but high humidity so it was less than ideal storage).
I loaded and shot the last of his primers (mainly cci, small and large) and powder left over from back then this year.
No issues. Can't tell any difference between the old and new except it seems like the newer cci's might seat a little easier.
Those primers will probably out live you!!
You can usually kind of read the primers by the boxes that they are in. If the cardboard trays that they are in are "Powdered" away, there may be some issues with the primers.
I have bought some old primers that the boxes were still intact, they always shot well..Bill.