San Francisco -- As college students begin to graduate this month, they and their parents are eager to take advantage of one of the first pieces of the new national health law to take effect, allowing young people to stay on their parents' insurance until they turn 26. When the country's largest insurers announced last month that they would offer this coverage before it becomes mandatory on Sept. 23, that was all the better. But the health overhaul is complicated -- and carrying out this provision may be as well. The insurers said they would offer coverage right away or by June 1. It's possible, though, that some young people will be left off their parents' coverage until as late as Jan. 1, health experts say. The timing, they say, may depend on the parents' employer policies -- the type of plan, the contracts the employer has with insurers, and the employer's renewal or 'open enrollment' dates. 'It's the issue right now,' said Paul Fronstin , senior research associate with the Employee Benefit Research Institute in Washington, D.C. 'That's because it's the most timely. ... People are aging out or becoming ineligible as a result of graduating from college this month.' Information is scarce because the law is new, and employers and insurers are still hammering out the details or are waiting for additional information from the federal government. Employers don't yet know how to charge for dependent coverage -- for example, whether to group young adults with other dependants -- and are unclear about other rules and definitions. The federal government is expected to release guidelines within the next few days, according to one human relations consultancy. Until then, 'a lot of folks may have to be patient a little longer then they would like, but there are a lot of logistics yet to be worked out,' said Aron Ezra , spokesman for Blue Shield of California, which is based in San Francisco. The insurers that said they would extend coverage before Sept. 23 include United Healthcare , WellPoint , Blue Shield, Cigna , Humana , Aetna and Kaiser Permanente. Young adults -- often referred to as the 'young invincibles' in health insurance lingo -- have the highest uninsured rate of any other age group in the United States. About 13.7 million people ages 19 to 29 years old lack insurance, accounting for almost a third of the overall uninsured population in the nation, according to the Kaiser Family Foundation. Research has shown that young adults aren't simply eschewing insurance because they think they don't need it, but often lack access or can't afford the coverage they're offered. They are more likely to work part time and for employers that don't offer health insurance, and are less likely than older adults to be married and get coverage through a spouse. With the average employee share of premiums for individuals rising from $334 a year in 2000 to $779 in 2009 , younger adults may be less likely to be able to afford their employer's coverage. Another option for young people is the federal Cobra program, but that is often price prohibitive. The new health law allows adults up to age 26 to stay on their parents' coverage as dependents, even if they no longer are full-time students or get married. The main caveat is they cannot have access to health insurance through a job. Parents who cover their children generally do so through their employer's policy, and the rules can vary. Some currently drop dependents at age 19 unless they are full-time students, while some cover dependents through age 23 or 24. About 30 states have laws extending dependent coverage, but California is not one of them. With the troubled economy, many 2010 graduates are struggling to find jobs -- let alone ones with health benefits. Some young people are able to buy a low-cost individual health policy, but that may not be an option for those with pre-existing conditions or anything else that mars their medical histories. Because of a pre-existing condition, 22-year-old Allie Swislocki felt pressured to immediately find a job after she graduates this spring from UCLA. She takes medications to manage an inflammatory condition but is otherwise healthy. 'It was a big worry for me, especially graduating into this job market,' said Swislocki, who grew up in El Cerrito and hopes to work in Washington, D.C. 'I didn't want to be stuck in a position where I felt I had to take a job I wasn't interested in just because I needed health care. The passing of this bill has been a huge weight off my shoulders.' Her mother, Ann Manheimer , is anxious to keep her daughter on the policy of her husband's employer but has yet to receive any information about how to do that. 'I was relieved, and now I'm not so sure anymore because I don't know how it's going to work,' she said. Other parents share Manheimer's concerns. San Leandro resident Jeffrey Stone said his son, who is almost 21, has been uninsured since he turned 19 and was kicked off the policy of Stone's employer policy because he was a part-time, rather than full-time, student. Stone said he plans to reinstate his son on his plan as soon as he gets the go-ahead from his employer. Employers often have different types of policies, so different rules may apply. For example, employers who are self-insured and pay their own health claims have more leeway than those whose risk and coverage is handled by an insurer or other third party. Some employers may be locked in contracts and thus restricted from extending coverage until their employees' policies renew. For Angela Cabral , the sooner these issues are resolved, the better. The clock is ticking for the 22-year-old graduate of the University of California at Berkeley, who will age out of the coverage of her mother's employer when she turns 23 in June. Cabral, of Walnut Creek, who is working at a law firm in her hometown while she saves money for law school, realized firsthand the value of having good health coverage when, at age 20, she had emergency abdominal surgery. While healthy now, Cabral doesn't plan on taking any chances. 'Just from my experience,' she said, 'I don't feel like health insurance is something I want to scrimp on.' 