We're used to looking at the expiration date on foods to know how late we can consume something, but according to Joanne Lacina, the founder of OliveOilLovers.com, we should be looking at the harvest date when it comes to buying olive oil. When an olive oil has a "best by" date, it could be anywhere between a few months or two years from the date of actual bottling. A harvest date, which also appears on olive oil bottles, tells you the exact date when the oil was pressed. This can give you a very clear indication of the age of your olive oil purchase.