Two things, good whisky in a good cask will usually age well for a long time while mediocre whisky in a mediocre cask will have mediocre to terrible results.
Either way, at some point in time the whisky will leach out too many tannins and other nasties from the oak and can ruin even an excellent whisky. Still 40-50-60 year old and older whiskys exist that remain more than drinkable but I believe these are exceptions rather than the rule. Most would be over the hill at some point before those kind of ages.
One of the skills of the distillery is to decide when the whisky is "ready".
Somewhere I read an article whose argument contended that cask management contributes 70% to the final quality of a whisky. I don't know enough on the subject to argue or agree but it is obviously critical to the end product.
Either way, at some point in time the whisky will leach out too many tannins and other nasties from the oak and can ruin even an excellent whisky. Still 40-50-60 year old and older whiskys exist that remain more than drinkable but I believe these are exceptions rather than the rule. Most would be over the hill at some point before those kind of ages.
One of the skills of the distillery is to decide when the whisky is "ready".
Somewhere I read an article whose argument contended that cask management contributes 70% to the final quality of a whisky. I don't know enough on the subject to argue or agree but it is obviously critical to the end product.