Most photographic chemicals will remain stable for a very long time if they are kept cool, dry and dark. There are exceptions - glycin is one example. I have sodium sulfite from the 1940's that is still ok, and some pyrogallol and hydroquinone from the same era that is ok as well.
I have previously written about the Phenidone I bought in the early 1970's (stored in amber glass containers) that is still fully active. I mixed some concentrated developer with it yesterday.
I also have potassium bromide that has turned into a facsimile of a concrete block - stored it in the wrong environment.