The White House said Monday that it was still unable to provide the demographic data is describes as a "key element" to evaluating the overall success of ObamaCare.
But the White House spokesman also pledged to make the data "available as soon as possible."
"If you look at how we've dealt with data as it's become available over the past several months, both good data and bad data, we've done our best to provide it to you when we are confident about the accuracy of it," Carney said.
Healthcare experts have warned of a "death spiral" if not enough young, healthy adults buy into the ObamaCare marketplace to offset the cost of insuring older and sick Americans. A study report by the Kaiser Family Foundation showed that 4 of 10 enrollees would need to be between 18 and 34 years old to prevent a rise in premiums in subsequent years.
Still, the same report found that if a quarter of enrollees fell within that age range, insurers would only need to raise premiums by 2.4 percent in 2015, and the ObamaCare legislation includes protections to account for some amount of imbalance among enrollees.
On Monday, Carney said that "obviously, a good mix is important" and touted efforts by the administration and insurers to promote health plans to young consumers.
"We're going to be, as we have all along, engaged in an effort to provide a product that is clearly very much in demand to all of the Americans who want to avail themselves of it," Carney said.
Separately, Carney downplayed a Congressional Budget Office estimate that 7 million individuals would sign up for insurance on the healthcare exchanges this year. Senior administration officials, including Health and Human Services Secretary Kathleen SebeliusKathleen SebeliusSebelius on GOP healthcare plan: 'I'm not sure what the goal is here' Obama's health secretary to be first female president of American University Leaked email: Podesta pushed Tom Steyer for Obama’s Cabinet MORE, have previously described hitting that number as a "success."
"It's important to understand that it is not — that there's not some magic number: 6,999,999 and the system collapses; one more than that and it functions perfectly," Carney said.
"We're not backing away from a number that we didn't put out originally," he added. "I think that others noted that 7 million is a fine target, but that that will not determine whether the marketplaces function effectively."