"... the changes that happen between 18 and 25 are a continuation of the process that starts around puberty, and 18 year olds are about halfway through that process. Their prefrontal cortex is not yet fully developed. That's the part of the brain that helps you to inhibit impulses ......."
Is this idea that the brains of 18 year olds aren't fully developed a matter of settled science?
Brain Maturity Extends Well Beyond Teen Years : NPR
So, technically speaking at 17 yrs of age his brain was only about halfway through the development process in some of the most critical areas of the brain. So having the same expectations of a 17 yr old when it comes to his ability to make judgments and control his behavior as you have from a man over 50yrs of age is like challenging a toddler to leg race. While we hope our kids are able to practice self control despite this disadvantage they often don't, especially boys. An inability to function at the same level as a man over 50 does not necessarily reflect the same on the character of that boy as it does of a man Dunns age.
Bottom line, I would have expected more from a grown man and Jordan Davis was just a boy.