Grain alcohol really never goes bad.
However once you open the alcohol including grain alcohol or any other alcohol the grain alcohol as well as many other alcohol types loses it's flavor overtime.
So in one way the grain alcohol does go bad because it loses it's flavor and has a different taste that may not be as good for you to drink.
However the grain alcohol never really spoils where it would make you sick if you drank it.
But it's best to drink the alcohol before it gets too far in age so that it has the best flavor.
If the bottle of grain alcohol has never been opened then the taste should be good for 10 years or so but it's best to drink the bottle of grain alcohol soon after buying it for the best taste.
However if you drank older grain alcohol it won't make you sick.