Under traditional insurance laws, the age at which a person was required to get their own insurance was left up to the individual insurance companies. Some companies set the age at 18, while others made it 21 and some even let a young adult remain on their parent's policy until they were 25. With the passage of the Affordable Care Act, called the ACA, that has changed, and the changes have been effective since 2010.
Under the ACA, health insurance companies are required, by law, to extend coverage for young adults who still live in their parent's home up until they are 26 years old. You are not required to be enrolled in college courses, but you must live at the same address. The idea is to make sure that young adults, who are notorious for having little or no income, are still able to receive medical care when they need it.
However, if you move out of the family home into your own, then you are required to find your own insurance. The reason for this is that the risks of insuring differ by your residential address. If you are under 26 and live in a college dorm or other university housing, you are still eligible for your parents insurance, but you may have to provide proof of college enrollment.
Additionally, the new laws will allow people with preexisting conditions to get health insurance. This portion of the law does not become mandatory until 2014, but many insurance companies are already altering their acceptance procedures. What this means is that millions of Americans with diabetes, asthma, heart conditions who have never been eligible for health insurance will now be able to get the coverage they need.