As I mentioned in my comment, I would be less likely to blame this on brain chemistry and more likely to blame it on lack of experience. While I have not reviewed the research, it would be very difficult to isolate a mental development pattern from all the other confounding variables of young drivers.
First, driving is inherently a procedural task. It takes time to develop those skills to the point of automaticity, so there is a somewhat higher level of attention and resources being devoted to the mere mechanics of driving.
Second, our ability to respond to dynamic situations is dependent upon our brain recognizing those situations and responding in a preprogrammed fashion. This is also something that cannot be learned other than through time on the road. For example, I learned that it is not a good idea to drive next to someone on the freeway, matching their speed, because they could suddenly decide to switch lanes. I learned that from experience, and it has helped me avoid numerous accidents.
Third, we have to consider the propensity of younger folks to want to engage in stupid things, like texting and driving. While people of all ages do this, there are plenty of reasons to point to younger generations being more active with their texting and other apps that can create major distractions.
Young drivers simply don't have the motor skills, coordination, and mental preparation that older drivers do. They also have more distractions. This doesn't mean that there are some young drivers who couldn't outdrive older drivers, nor does it mean that all older drivers are reasonable drivers. There is a lot of variation.