One of the keys to the success of President Obama's health care law is that enough young and healthy individuals must sign up for insurance to offset the cost of covering older and sicker participants, particularly those with pre-existing conditions.

But the first demographic data released by California on Thursday show that a disproportionate number of those picking a plan in the first month of the state exchange's operation were older.

The report by Covered California, posted by Dan Diamond of the Advisory Board, revealed that 34 percent of those who picked a plan in October were age 55 to 64 and 22 percent were age 45 to 54, even though those age groups represent just 11 percent and 14 percent of the California population, respectively.

In contrast, as demonstrated in the chart accompanying this post, younger groups were represented among participants in Obamacare roughly in the same proportion as they represent of the state's population.

Covered California, the entity overseeing the state's exchange, noted that many of those who are younger than 18 qualify for support through Medicaid, which is measured separately.

Californians between 18 and 34 represented a combined 23 percent of those picking a plan.

There are a number of ways to interpret these numbers. The optimistic way is to argue that younger people with lower medical costs are likely to wait to purchase insurance, perhaps until right before the end of the open enrollment period that extends through March 31. In a statement, an exchange official called the numbers "encouraging."

A more pessimistic way of looking at the data is to note that Obama administration officials had said before the start of the health care program that roughly 40 percent of the expected 7 million enrollees had to be from the young-and-healthy demographic.

In addition, it's important to keep in mind that California's website has been functioning more smoothly than the federal website serving residents of 36 states. For the health care law to be successful nationwide, exchanges in each state need to have the proper balance of young and healthy customers.

It's also worth keeping in mind that age is only a rough approximation of what the risk pool looks like because what ultimately matters are medical costs. Some individuals can be young and sick, others may be old and healthy.

The Department of Health and Human Services hasn't yet released a nationwide demographic breakdown of those who have signed up for plans through Obamacare's exchanges.

Both the federal government and California have counted individuals as "enrolled" if they went through the application process and selected a health insurance plan, regardless of whether they have yet paid the first month's premium, which is how enrollment is typically measured.

Individuals have until Dec. 15 to pick a plan and until the end of December to pay for their first month's premium to be considered insured by Jan. 1.

In separate news, California regulators said they would not go along with Obama's proposal aimed at allowing individuals to remain in insurance plans that do not comply with new rules imposed by the health care law. Obama has been under fire as a wave of policy cancellations by insurance companies contradicted his promise that those who liked their health care plans could keep them under his legislation.