At any PX.
Yes - they are food products so deteriorate over time.
It is available in 190 proof (95% alcohol) and 151 proof (75.5% alcohol) varieties.
alcohol doesn't expire exactly but it does go stale
instilled spirits, once in the bottle, really don't age. If it's an unopened bottle, it's still good (but not necessarily better or worse than when it was bottled). Liquors have sugars and sometimes...