Demographics, as Peter Drucker famously pointed out, is one of the seven sources of entrepreneurial opportunity. Why are demographics so important? Consider the quality and quantity of the U.S. labor force. Birth rates largely determine the size of the future workforce, and the numbers of younger and older people affect public spending on education. What's more, patterns in marriage and child-bearing affect the labor force, and migration and immigration alter the mix of job skills, languages, and cultures in the U.S. workforce.

While business and government must react to these trends,...