Old salt will not make you sick and it's safe to eat.
The salt is already thousands of years old anyway before it was extracted from the earth so you're actually eating old salt when you buy it and use it.
The salt cannot spoil although the salt may become hard overtime but that does not mean that the salt is bad or unsafe to eat.
You can just smash the salt back up and use it for a very long time.
Salt cannot spoil or go bad like other foods that grow bacteria and make you sick because for foods to spoil, fungal, bacterial, yeast or other microbial growth has to take place and with salt that cannot happen.