People don't normally go through their seasonings or spices very quickly, so they wind up sitting in their cabinets for years and that can be a problem. The largest spice company in the world, McCormick, recently explained how to tell if your seasonings are too old for consumption.
If you discover that you've got some really old seasonings, don't worry! They aren't going to make you sick, but it's probably in your best interest to not use them anymore since they aren't going to be effective. When spices or seasonings age, they lose their flavor. Therefore, adding old spices to your dishes is pretty pointless.
An easy way to tell if your spices or seasonings are old is if they are housed in a rectangular tin or if they were packaged in Baltimore. If that's the case for you, congratulations, your seasoning has been around for a quarter of a century!
McCormick also recommends making sure your spices have a strong aroma and taste, as well as a vibrant color. It's also good practice to replace them every three years.