Whiskey

Most whiskies have an optimum barrel time of far less than 50 years, most people presume that age=quality. It is not true , although  whilst in the cask, there are two actions taking place. Yes, the cask is breathing and hence the spirit is reacting with air.

But at the same time, the whisky is also in contact with the wood, meaning that the spirit is continuing to mature and react with the wood, it is not neccesserily a good taste after a while.

It really depends on which type of whiskey you mean.

 Bourbons generally should be aged less than scotch or Irish whiskey.  This is because they can only use brand new charred white oak barrels.  There are only a handful of bourbon aged more than 15 years.  Some are really good, but some of them too have been aged for way too long and the barrel flavors overpower the grain.  I don't know of any bourbons on the market aged over 23 years.

As for scotch or Irish whiskies, it can really vary.  However, because they reuse barrels, they usually need more time aging to mature.  This is why many scotches are aged 25 years or longer.  

You can read more about Kentucky bourbon whiskey at Bourbon Central.