China is coming. It’s an unstoppable financial juggernaut. It will soon overtake America.

That’s according to just about everybody looking at China’s GDP growth. The country has managed to grow their economy by nearly 10 percent per year on average in the last decade alone.

Relax. We’ve heard this before. And while it might be true, it might take longer than you think. Or it might not even happen at all.

Remember when Japan was buying everything in sight in the 1980s? Many thought that their economy would overtake America’s by the end of the century. But those fears never materialized. Japan crashed, and the country is arguably starting a third “lost decade.”

Why? Because of one non-financial trend that has a huge impact on long-term investments. I’m talking about demographics. Japan’s reversion to slow growth can be attributed to an aged population.

According to the CIA World Factbook, the median age in Japan is 44.6 years, while in the US, it’s 36.8 years. The retired segment of their population makes up a larger percentage than it does in the US (at least for now). Only Mexico has a larger median age.

China and Japan have a lot of differences, but the demographics in the Middle Kingdom suggest that China’s rapid growth must decline. Things may appear to be going full speed ahead, but China faces a tremendous crisis in the decades to come.

That crisis stems partially from China’s infamous one-child policy. It’s led from a fertility rate of 6.1 in 1955 to 1.8 in 2010. Essentially, the average female has gone from producing 6 children to around two on average. Ironically, as China becomes wealthier, more women there are viewing reproduction as an impediment to affluence.

Understanding a country’s demographic trends adds other compelling criteria to look for in any investment. Following the baby boomers in the United States, for example, one might have invested in Kimberly Clark for diapers in the 1940s, Mattel and McDonald’s in the 1950s, financial services in the 1980s, and in healthcare and health care REITs today.

China continues to build the infrastructure of the first-world country that it aspires to. There are plenty of investment opportunities there that have nothing to do with demographics.

World population is expected to hit seven billion by the end of this month. Longer-term projections indicate that this growth is starting to lose its legs. Within a century, global population may actually end up lower than it is today.

Identifying demographic trends and changes to those trends can provide a simple way to screen for companies to own for long-term investment success.