That might be true, but this paper is wildly unconvincing. Cross-country comparisons have way too many confounding factors. Not least that economic growth reduces population growth.

As for an aging population slowing the economy, Japan is the classic example of the dynamic: https://unchartedterritories.tomaspueyo.com/p/why-japan-succ... Looking within-country during a retirement boom seems more informative than trying to compare apples to oranges.