If using the asvab as a determinant remove the HS diploma requirement and use the asvab to restrict eligibility. Some 16 yo can be quite intelligent. Also wouldn’t hurt to make the military be the military again. I see more machismo in high school sport teams. Why enlist to serve with a bunch of pajama boys?
Also I enlisted at 17, graduated high school then went to Navy boot camp. Stayed 20 years. I was a recruiter and boot camp drill instructor So I got to see both ends of the equation. Some very smart college grads were boxes of rocks and some non grads were excellent sailors