Teen drivers often take chances behind the wheel. Those pushing for tougher teen licensing laws now say the latest science may help explain why.
Researchers studying the brain say the last section to develop -- the frontal lobes -- may not mature until a person is age 25 or beyond.
"The frontal lobes are sort of the executive center of the brain -- the part of the brain that's responsible for planning, organizing, anticipating the consequences of one's actions," said Elizabeth Sowell, a UCLA neurophysiologist.
The research was cited by Virginia lawmakers who are pushing a bill to ban cell phone use by young teen drivers. A similar bill is up for debate in Maryland, along with a proposed measure to limit the number of passengers who can ride with a teen driver.
"The studies point to the fact that teens are taking the highest risk because in some respects the brains don't know any better," said William Bronrott, a Democratic legislator representing Montgomery County in Maryland's House of Delegates.
Researchers are quick to point out more study is needed to prove that what's happening in the teen brain directly impacts behavior.
But at Philadelphia's Temple University, researchers found young drivers were more likely to make risky decisions if their friends were present. For teen drivers, the risk of a crash doubles with just one extra passenger, the study found.
To lessen the chance of an accident, experts say parents should communicate with their teen while traveling together, invest in extra behind-the-wheel driver education, meet the teen driver's traveling companions, choose a safe car and ride periodically with the teen driver.
"Interestingly, the teenagers didn't take more risks when they were by themselves," said Lawrence Steinberg, a psychology professor at Temple University. "It was only when they were in the presence of other kids."
It's another reason why lawmakers in 13 states are now trying to limit the distractions that lead to unsafe teen driving.
ABC News' Lisa Stark filed this report for "World News Tonight."