Bourbon bottle from the 19th Century.
Distributed in practice almost all Bourbons today contain more than two-thirds corn, have been aged at least four years, and not as "straight bourbon"-with or without the qualifying "Straight Bourbon" label. [Edit] The exceptions cheaper standard bourbon brands (at the age of three years) and pre-mixed cocktails made with straight bourbon is aged for two years. But at least a little bourbon distillery are markets for less than three months old.
Whiskey sold as Tennessee whiskey committed as Bourbon under NAFTA  and at least one other international trade agreements defined, and is the legal definition of Bourbon under Canadian law to be just, but some Tennessee whiskey makers not describe their product as Bourbon and insist that it is a different type of whiskey when marketing their products.