I take it this is the Air Cadet Pilot Scheme, 12 hours flying and ground schooling with the aim of going solo by the end of the time.
To avoid covering old ground you could read from here down ACPS Cancelled: another kick in the teeth - #190 by Giminion a lot of unsubstatiated guesses in the thread though and I would take those with a pinch of salt.
Long story short something happened, it was investigated and the outcome has been over 18 for ACPS going forward.
Edited to add
This may explain why your grandsons assessment hasn’t been cancelled, still no guarantee of him getting a place but good luck to him and well done for getting through the initial sift 