Complex sentence: It is blended from 1200 eaux-de-vie, some more than a century in age, then it is aged in tiercons, oak barrels that are several hundred years old, in its own cellar.
Split into simpler sentences: It is blended from 1200 eaux-de-vie, some more than a century in age. Then it is aged in tiercons (oak barrels that are several hundred years old) in its own cellar.