Culp is available to MS1's. If he hasn't started the application he will need to start soon, the deadline is the beginning of November...the 4th I believe. Once the application is complete the PMS will review the cadet to give his recommendations and complete the application process. The applicant will also need to complete his security clearance as well. I'm not sure how other battalions do it but for my son's the PMS sent out an email to only the cadets he wanted to apply. Only the applications that have the PMS recommendation will have there applications submitted to the Brigade, at least that's the way son's battalion works.
Have your son contact his battalion HR person about the application process, tell him not to wait too long.
I agree, it is highly unlikely he would be sent to Airborne or Air Assault.