X.O. (or extra old) Cognacs previously required a minimum of six years aging for the youngest cognac in the blend, with the average age running 20 years or older. All Cognac houses maintain inventories of old vintage Cognacs to use in blending these top of the line brands. The oldest Cognacs are removed from their casks in time and stored in glass demijohns (large jugs) to prevent further loss from evaporation and to limit excessively woody and astringent flavors.

As of 2016, according to the official Cognac regulatory agency, BNIC, the minimum component age requirement for X.O. Cognac must be 10 years from 2016 onwards. In practice many Cognac houses and brands had been at or above the 10 year requirement for their X.O. expressions, but this is now the legal requirement.