Cars are involved in 50% more deaths than guns. About 1/3 of car fatalities involve a driver under age 21. Most lethal car accidents involve multiple casualties. If it's unreasonable to allow someone under 21 to handle a handgun, it is positively insane to allow them behind the wheel of a car, with 6 million times the potential energy, where a SINGLE error or act of will can kill dozens.
No reasonable person can object to raising the driving age to 21, and improving our background checks--no one with a history of mental illness or psychotropic drug use should ever be allowed to drive a car. Likewise, anyone with a history of anger-related violence is a threat to those around them.
Ultimately, we need to ask the hard question: Who really NEEDS a car? Certainly urbanites with access to mass transit have no need for a personal vehicle, given the inherent dangers and cost to society.
The fallacious response to this is to argue that "cars aren't meant to kill." But, if they are not meant to, but are 50% more lethal than handguns, no reasonable person can argue against tighter restrictions.