Like with OPs question as far as I know people cannot be much help due to it depending on branch, how long its been since recruit test and when the allocations take place.
I think you are given a date for the PRNC after you have been allocated a place at Raleigh. The PRNC will be a few months before Raleigh and so depending on branch it could be years or months till his course.
Best thing to do is just get your son to call the AFCO in a few days (to make sure they've recieved the PJFT) and ask about if they have a predicted Raleigh date, predicted PRNC.
They will probably tell you something like "its gonna be X months but you will know for sure because they are allocating in x month"