Final answer:
High-income countries in Europe and Japan are the most affected by an aging population, leading to a decreasing worker-to-retiree ratio and a higher dependency ratio.
Step-by-step explanation:
The region of the world most affected by aging and thus by a steadily decreasing worker-to-retiree ratio is the high-income countries, such as those in Europe and Japan. These nations are experiencing a demographic shift where the elderly population forms a larger share, while the number of younger workers is declining. This shift results in a higher dependency ratio, which pressures the labor force and economic growth, as there are fewer workers to support a growing number of retirees. For instance, China is expected to see nearly a third of its population aged sixty or older by 2050, leading to significant challenges in maintaining its workforce and sustaining economic performance.