I think your son will be OK. Average gpa is just that average, they take some above and some below depending on the other things....like NJROTC Leadership, Athletics, Community Service, SAT/ACT scores, and Class Rank. When you look at the SA "averages" that is the middle 50%, so as long as his gpa is not 2.0 or below or if he takes AP/Honors/IB Classes even a 2.0 unweighted is fine because the advanced classes weigh at either 4.5 or 5.0 so his weighted GPA would be a lot higher.
The NJROTC (if he is applying to the Naval Academy) is a huge plus for them, especially the XO Role...Leadership, Leadership, Leadership..... Did he get asked to interview in person? I know the CGA does that with all "Highly Qualified Candidates".