Brandy and whiskey are the most common liquors that require aging and are required to spend a minimum (typically 3 years) amount of time in barrels prior to bottling. Many rums and tequilas are aged as well, though aging is not a requirement for all styles of these liquors. Higher quality spirits are aged for a longer period of time and have a price tag to reflect this extra mellowing time.
How to tell the age of alcohol?Not all distilled spirits are aged and some must meet minimum requirements to be placed within a certain class. For example, single malt Scotch and Irish whiskies must all be aged for a minimum of 3 years and añejo tequila must be aged for at least 1 year but no more than 3 years before it is considered an extra añejo. Other spirits such as rum have no requirements for aging and vodkas and gins are typically unaged.
Many times, especially in the case of whiskey, the label will indicate the liquor's age. The is particularly true when the brand wants to show off how old the bottling is. Other labels do not indicate an age at all and this is often because the distiller relies on a general time the liquor spends in a barrel, and will fine tune it according to taste. A fine example of this is Maker's Mark, which is aged for nearly 6 years and at that mark it is tasted and aged further if needed "until it is fully matured."
What about blended spirits?If a blended liquor (rums and whiskies are most common) is marked with an age statement on the label it typically means that the youngest liquor in the mix is that old. For instance, the Chivas 25 Year Old Scotch bottling is comprise of a blend of different whiskies that have each been aged for at least 25 years, though some may be older than that.
Why are whiskies aged so long while rums and tequilas are aged for so short?The simple answer is climate. Think about the climate differences between the major whiskey regions like the United States, Canada, Ireland, and Scotland versus Mexico where tequila is produced and the Caribbean and South America where the major of rum is made. The climate of the region is the main factor in how long a spirit needs to be aged to its optimal potential.
In hotter climates the aging process is sped up naturally so it is unnecessary to keep tequila or rum in barrels for more than a few years. Tequila reaches a peak at around 2-3 years and rum averages about 8 years. In the case of rum, however, the time is going to depend significantly on the location it is produced, which can be anywhere in the world.
In contrast, the majority of the whiskey and brandy distillers are located in the northern hemisphere in locations that experience significant annual shifts in temperature. The extreme cold and heat and mild periods in between require a longer time in the barrels in order to obtain the correct mellowing and barrel notes in the whiskey. You will notice that the more northern the whiskey the longer it is aged.