What are the factors that determine how long whisky is aged? Whisk[e]y varieties often have significant differences in how long they are aged.  While there are always exceptions, Bourbon is often aged for 5-10 years. Scotch, on the other hand, is more commonly aged for 10-20 years.  Why is this?
Aging or 'Finishing' is an extension of the maturation process, when the spirit is subsequently filled into empty casks that previously held other
wines or spirits for a further relatively short period at the end of maturation.


  The selection of casks can affect the character of the final whisky.
  Outside of the United States, the most common practice is to reuse
  casks that previously contained American whiskey, as US law requires
  several types of distilled spirits to be aged in new oak casks. To
  ensure continuity of supply of used oak casks some Scottish distilling
  groups own oak forests in the US and rent the new barrels to bourbon
  producers for first fill use. Bourbon casks impart a characteristic
  vanilla flavour to the whisky.


so really the longer you age the whiskey the more of the flavor you are going to capture form the cask