It depends on several things. Usually about 2 years is the longest you would want to leave anything on the shelf, but 1 year is probably better if you're real picky. I would bet that plants would still do well with stuff that's been sitting around for 5 years, depending, but I would not use nutrients that old. Organics don't last as long as non organic.

In my younger days I made the mistake of buying gallon containers of nutes because they were cheaper. Now I'll only get quarts, except for SuperThrive, of which I get a thimble full.