1. Increased life expectancy: Advances in healthcare, better living standards, and medical technology result in people living longer.
2. Declining birth rates: Lower fertility rates mean fewer young people are being born, so the relative size of the younger population decreases over time.

As the proportion of older individuals (typically aged 65 and above) grows, it affects a country's economy in several ways:

1. Economic growth: With fewer workers relative to retirees, economic growth may slow as there are fewer people contributing to productivity.
2. Public finance pressure: Governments face higher costs in providing pensions, healthcare, and other age-related services. At the same time, with a smaller working population, there may be less tax revenue to fund these services.
3. Labor market impact: A shrinking workforce can lead to labor shortages, driving up wages, or causing businesses to automate or look for labor-saving technologies.
4. Savings and investment patterns: Older people tend to save less and spend more on healthcare, which may affect national savings rates and investment patterns.

Countries like Japan, Germany, and Italy are examples of nations dealing with ageing populations, and many other countries are expected to face similar challenges in the coming decades.