Sincere question: don't most if not all Western nations have essentially the same problem, to a (perhaps?) lesser degree?

I am far from being an economist or political scientist, but that's what it appears to me. Every government I can think of puts its collective thumb on the scale in the economy somehow. And I can't judge which of the metrics cited (negative productivity growth, fertility below replacement, etc) are causal and which are incidental. So I don't understand how the claim is supported by the data.

Or is the entire piece just somebody's opinion with an agenda? I'd love to hear from someone unbiased who knows better.

Yes. There’s nothing particularly special about Australia that he’s pinning his argument on.

He also does have an agenda—the Laffer curve nonsense kind of gives it away—but I sincerely doubt that the extravagantly wealthy are going to swoop in and save the billion-plus elderly people that are going to find themselves priced out of living in the future this economic model predicts. Certainly not out of the goodness of their collective hearts.