When is a kid not a kid anymore?

If you asked my 12-year-old daughter, the magical age would be 13 — the age when you're officially a teenager and can no longer be considered a "child." If you asked my 15-year-old niece, the age would be 16 — that's when she will be able to drive a car and get an after-school job. According to the U.S. government, a child officially becomes an adult when she turns 18. That's when she can vote and start paying taxes. But interestingly, even though an 18-year-old can go to war, the government does not consider that person mature enough to drink alcohol. The magical age for that rite of passage is 21. Still, even a kid who can go to war and buy a beer is not old enough to rent a car; for most car rental companies, the minimum age for rental is 25.

As it turns out, the folks at Hertz or Alamo may have a better idea about the age of maturity than the U.S. government. According to the latest research, the human brain does not fully develop until around age 25. And it's those last few years that are critical when it comes to things like impulse control and risk taking.

In studying scans of the adolescent brain, neurologists have learned that when kids are around the age of 18, their prefrontal cortex is only halfway developed. This is the area of the brain that helps control impulses, solve problems, regulate emotions and organize behavior. That's not to say that kids in their late teens and early 20s can't take on these tasks, but it does mean that it's harder for them to do — at least until around age 25 or so when this area of the brain fully develops.

This isn't exactly a news flash for generations of parents who have watched their teens take crazy risks while seeming unable to get their lives together until they hit their mid-20s. For the average teen growing up in a supportive family (and I mean emotionally and financially), the latest findings are not really a big deal. Moms and dads will continue to bail out their college-aged kids if they get themselves in a mess.

But this information sheds new light on the way kids without as much support are treated. In the foster care system, once a child turns 18, he is considered an adult and can no longer receive state-sponsored support. And many people think this is way too early for a teen to be on his own, especially a teen who has experienced an unstable childhood and who may be more likely to have problems controlling impulses than his peers from more stable homes.

Because of this, some foster care advocates think it makes more sense for 25 to be the new legal age of adulthood. They want the age of maturity to be based on science, not arbitrary numbers.

I'm not sure that this concept will fly with my 12-year-old, or even my niece. But then again, when they mess up in their teenage years, my family will be there to (hopefully) pick them up and get them back on their feet.

Not all teens have that luxury.

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