The thing about the military is that it is always there. I enlisted just out of high school and started completely at the bottom. If I had finished even one semester of college, I would have started at a higher rank. Let him do the first term and see how he goes.
I was a terrible student in high school, with very little motivation, but 4 years in the Army gave my brain time to catch up, the Army taught me how to learn and I saw that the people without college degrees were cleaning the toilets while the people who had college degrees were watching us do it.
I got out of the Army, and using credits I'd gotten in the Army, graduated university in 2 years - no more cleaning toilets for me