The International Monetary Fund is calling on Asian economies to learn from Japan's experience and act early to cope with rapidly aging populations, warning that parts of the region risk "getting old before becoming rich."

Asia has enjoyed substantial demographic dividends in the past decades, but the growing number of elderly is set to create a demographic "tax" on growth, the IMF said in its economic outlook report for the Asia-Pacific region released Tuesday.

"The speed of aging is especially remarkable compared to the historical experience in Europe and the United States," the IMF said. Per capita income in Asia relative to the U.S. remains at much lower levels than those achieved by mature advanced economies in the past.