Larry - While producers have gotten pretty good you can't say with certainty how long a barrel can age before it is past it's prime. IMO once you hit 40 years with almost any scotch you start taking your chances which is why the barrels selected for extra aging are checked and tasted so regularly once they hit the 30 year mark. Obviously they are checked before that but more attention is payed to them if going to be held for a long time.
I've not had 30 yo samples from every distillery but the majority of them and some have done better than others but the limited amount of samples of whisky that old from a fair number of distilleries prevents me from saying that any distillery can't or doesn't produce good old whisky.