Unfortunately you've missed the point entirely. The arguments you are addressing are not about operations - what planes are in service, when and why. I get that's your focus and understand that; however there is another world - finance and securities - out there . 'Average fleet age' is but one of many metrics that allow comparison of a single airline over time or between airline peers; its a broad management/corporate/strategic metric. Airlines too use it for various reasons - Qantas have said they no longer value it - but they previously did use it more openly and I bet they still tally it.
Exactly! But analysts and others then ask -
what has brought these trends about and, in the newspaper articles' cases, the
timing? As I said above, it might be for perfectly understandable reasons - Covid and the cessation or slow down in aircraft production would be one to increase an average age - but it might be for other reasons, and that's the type of analysis I and the journos are talking about. If you combine a trend in average fleet age with other measurements, someone might come to a more pessimistic view of a particular airline.
So what? Well, if you are a shareholder, you may choose to sell or hold on. Your super fund may choose to sell or hold on a big bunch of shares that may affect the price. A ratings agency might mark down the company's debt rating a notch. Or, it might go the other way if the metrics look good.
I've tried to explain why its measured by several sectors outside the airlines and that its just one metric among a bunch. Within an airline you can bet that
someone keeps tabs on this, and the same measurements for its peers. Its at least like an airline will keep tabs on when its peers last refurbed its business cabins etc, what seat pitches are used on equivalent aircraft types, at least to see if its getting out of whack with peers. Of course it gets factored into decisions on procurement and its not 'stand alone'. Anyone running a fleet of anything will want to know what the average age - or hours on the clock - is, amongst other things.
I think its completely unremarkable that average fleet age is measured and used by various groups - including airlines - as part of a picture of the overall health of the entity. The more in-depth analyses would try to drill down to flight cycles/hours etc. The journos used this one measure in a narrow way, looking at management decision-making and timing of significant capex.