"Whichever way you look at it these aircraft are getting old."
Great sweeping generalisation which just begs to be flamed!
So you'd feel the same way if the BBMF disbanded due to the age of the aircraft? Not to mention all the private WWII warbirds; on the commercial side Buffalo airways would be mightily irked as would all the private DC-3/C-46 owners.
It's about maintenance, implementing and legislating said maintenance and finally cost when the cost of the above makes it financially non-viable.
Displaying aircraft has become a safer spectator experience, having said that most spectators are aware that this, in common with all aviation related activities isn't without risk.
When spectators vote with their feet (or their pockets) all bets will be off.