Your average 16-year-old male these days is not as mature as the average one 50 years ago. I’d rather see a renewed focus on getting teens in shape, which would presumably make a significant chunk of those “17- to 24-year-olds who are ineligible to serve” eligible.
18 should be the minimum age. I don’t want to see 17 or 16 year old kids in the military.
There’s a considerable chunk of the already serving that are not even close to being in shape for anything other than sitting behind a desk.