Millennials arethe most populous generation in America.

From a demographic perspective, this is very good news for the nation. It means the U.S. has a wave of people just entering the workforce, whose tax dollars (hopefully) will support the retirement of the baby boomers.

Lots of other developed countries aren't so lucky. In Japan and many European countries, boomers (people ages 50 to 68) outnumber millennials (ages 14 to 33). Those countries may have a harder time maintaining the social safety net for the elderly as the ratio of retirees to working adults rises.

The demographics of less wealthy countries — like, say Mexico — look quite different. There, the young vastly outnumber the old.

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