He won't be scheduled to take the DoDMERB exam until he has completed a certain amount of his application to West Point. That is what triggers the go ahead for the DoDMERB exam. At that point, it's as ROTC-dad said, you will get correspondence from CONCORDE which will instruct you on how to proceed.
Yes - it is true that you want to start the DoDMERB process as soon as possible, but you can't start it on your own. You have to wait until West Point starts the wheels turning, which they won't do until your DS completes a certain amount of the application. This is because WP is allotted 'X' number of exams and they don't want to waste an exam on someone who isn't going to complete their application.
For most candidates, the application won't open for them until this week.
DoDMERB will only give you gray hairs if there are medical red flags. Then you go through the process of a remedial (they want more information), then based on that, they will qualify or disqualify. If the verdict is to disqualify, then it is up to West Point to decide whether to pursue a waiver. This process can take months.
If there are no medical red flags, then qualification can happen pretty quickly, especially early in the process.