The number of new U.S. start-ups per 100,000 individuals was about 185.6 businesses 20 years ago in 1991, according to data from Kauffman and the U.S. Census. New start-ups per 100,000 people declined 29.3 percent, to 131.3 for 2011, the most recent year of figures available.
"That raises some concerns about what's going on," Stangler said.
Few start-up visas and rising student debt
Start-up trends naturally reflect population changes, including aging baby boomers or those born after World War II. But Kauffman research shows older entrepreneurs aren't being replaced fast enough with younger upstarts.
Barriers preventing younger workers from becoming the next Mark Zuckerberg or Elon Musk include limited visas for skilled workers and rising student debt levels, Stangler and other economists say.
Overhauling U.S. immigration law has been long-awaited for years. But lacking political consensus, start-ups have struggled to absorb high legal fees associated with acquiring visas. And the months-long hiring process can delay key business decisions as they wait for visa lottery outcomes. Workers in high demand include engineers, computer scientists and software developers.
Visas are key to growth because immigrants are more likely to be entrepreneurs and create new jobs, says Donald Marron, director of economic policy initiatives at the Urban Institute. Marron is among those pushing for more start-up visas.
Of the engineering and tech companies founded in the U.S. between 2006 and 2012, 24.3 percent had at least one key founder who was foreign-born, according to Kauffman data. In Silicon Valley, the number was 43.9 percent.
(Read more: How lack of immigration reform harms start-ups, US economy)
Another speed bump to more new businesses and job creation is rising student debt. Exorbitant loan payments can deter young professionals from starting businesses.
President Barack Obama and the administration are pushing for student debt loan reform in which payments don't exceed more than 10 percent of an individual's income. "We need to abolish these fixed student loan payments and move toward income-contingent loans," said Gene Sperling, director of the National Economic Council.