Yes, they are OK to use. If they have been kept in a sealed pack, they will be less affected by age. The most common thing you will see in a propellant like White Lightning with a significant metals content is some oxidation on the surface of the grains. If it happens, you will notice it as white spots. To remove it, simply sand the grain's surface with a coarse paper like 80 grit. This exposes a fresh propellant and will make the grains much easier to light.
I have flown motors that were as much as 17 years old so far with no problems and would not hesitate to fly ones older than that if they had been stored under reasonable conditions.