Was that the one saying, "you would expect a large generation to be poorer than a subsequent smaller generation because of more intragenerational competition, but actually the larger generation can use politics to favor themselves precisely because they are more numerous?"
https://youtu.be/PkJlTKUaF3Q
The situation is even more extreme in places like Italy where the young are even less numerous compared to the old than in the UK.
It's the political equivalent to deflation. If every generation is smaller than the last, you end up with a gerontocracy and no-change society. To maintain pro-growth policies, you need a critical mass of young people who embrace change and want to grow. Otherwise you get stuck in a positive feedback loop of more and more power and money concentrated among the old which depresses the birthrate.