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One in four Obamacare enrollees are young adults. That’s below the target.

The Obama administration has just released the enrollment report that health wonks around the world have anxiously awaited: The one that shows the age breakdown of people selecting insurance plans under Obamacare.

It shows okay news for the White House: Twenty-four percent of those purchasing coverage are young adults, the coveted age group between 18 and 34 -- the exact group the White House thinks it really, really needs to enroll to make the health-care law work.

This is below the White House's target. The Obama administration has previously said that if 7 million people enrolled in coverage as expected, 2.7 million of them -- or about 40 percent -- would have to be young adults. That's an important target to hit because more young adults in the exchanges would mean a more healthy population, whose premiums could help subsidize the health care of older and sicker enrollees.

Even more important than these top-line numbers is what's happening in each state. Insurance rates are set on a state-by-state basis, so even if thousands of young people are signing up in California, it doesn't effect the premiums in neighboring Nevada.

The new Health and Human Services report does show some variation by state, although most exchanges tend to hover somewhere in the 20-percent range. In the District of Columbia, 44 percent of enrollees are young adults, the highest for any exchange (and remember: This is just the individual marketplace, not the small business exchange where Congressional staff shop). Arizona and West Virginia have the lowest rates of young adult sign-ups, who make up 17 percent of their marketplace.

Who runs the marketplace doesn't seem to make much of a difference: In state-based marketplaces, 25 percent of enrollees are between 18 and 35, compared to 23 percent in the federally-run sites. They do vary a bit by state.

Generally, young adults are signing up a rate disproportionate to their share of the uninsured population eligible to shop on the exchange. Kaiser Family Foundation estimates that about 40 percent of people who lack coverage are between 18 and 35. So, at the current moment, young adults are underrepresented in exchange enrollment. (The White House does make the case that young adults are represented proportionally when you look at overall population figures, not just those of the uninsured.)

Is 24 percent of sign-ups coming in among young adults bad news for the Affordable Care Act? It is, obviously, lower than the targeted 40 percent. At the same time, it's also higher than where Massachusetts's young adult enrollment started back in 2006, when the state expanded coverage. It saw young adult enrollment steadily grow, over the course of open enrollment, to make up a larger chunk of overall sign-ups.

And during December, there was an eight-fold increase in young adults selecting plans through the exchanges, which does suggest a decent number of shoppers were waiting to purchase coverage until the third month they could sign up.

Most health policy experts generally expect younger and healthier adults to wait until the end of open enrollment, which runs through March 31, to purchase coverage. Whereas those who are older and sicker would have immediate health-care needs and would jump at the chance to buy coverage, healthier shoppers would likely be more comfortable waiting a few months -- saving some money by not paying premiums -- and purchasing coverage sometime in the late winter or early spring.

"All evidence suggests the pace will increase," says Aaron Smith, executive director of pro-health law group Young Invincibles. "Young people want to explore their options before they make their decisions. "I think the 24 percent number suggests we're on the right track."