You can age beef for an almost unlimited amount of time. The meat has to be in a temperature and humidity controlled environment.  ...what my butcher's does is that is starts the process out with various alcohols (bourbon is good, because it has pungent flavours) and let's the meat age slowly. I can get 365-day aged steaks, but at a price. I've only done 180-day and 120-day, plus 90-day aging, which is offered in most butcher shops.