Is your son currently a freshman at college? If so I suggest he have a discussion with an officer in the unit who can answer all his questions. He needs to ask how to become a college programmer there, scholarship opportunities, etc.
If he is in high school he should start an NROTC scholarship application now. Heck, if he's a freshman with less than 30 credit hours he should apply now as well, but still meet with the unit.
In either case he can join the unit as a college programmer this spring. He'll have additional opportunities for a scholarship as a participant. He may have to double up and catch up on some training, but folks have done it before.
My son started as a college programmer his first semester and was awarded a scholarship during his sophomore year. If my son can do it then your son, if he is willing to put in the work, can do it too.
If you have more specific questions or concerns,, folks can answer them here