Owing to nicotine, PG (Propylene Glycol), and VG (Vegetable Glycerin) components, an e-liquid has a lifespan of 1 to 2 years. As time passes, nicotine oxidation and flavor degradation occur. E-juices that are old tend to have less nicotine with a lighter flavor.   As for the e-liquid expiration rules and regulations (the extent of the expiry date, display, and advertising), legal mandates...