The White House and its allies are in the midst of an aggressive push to get young adults to enroll in coverage through the exchanges.
Bringing young, healthy people into the system is key to holding down the premium increases that could come from guaranteeing coverage to older, sicker patients who have been unable to buy insurance in the past.
If the administration can successfully educate young people about their new options, Commonwealth said, ObamaCare can do a lot to help them: 82 percent of young adults who were at least temporarily uninsured this year will be eligible for some level of tax subsidies, or for Medicaid if they live in a state that is participating in the law's Medicaid expansion.
Commonwealth said the number of uninsured young adults has already fallen because of the Affordable Care Act. The law allows young people to stay on their parents' healthcare plans through age 26.
As of March, 51 percent of adults younger than 26 had either joined or stayed on their parents' healthcare plans — up from 47 percent in 2011.
Awareness of the provision has also risen steadily. Sixty-two percent of eligible young adults were aware that they could stay on their parents' plans this year, compared with 59 percent in 2011.