Your son is young, likely too young.
I “failed” my first assessment at 17 also.
What I hadn’t learned at that stage yet is to get an overview of the situation and context.
This wasn’t the academy being ‘unfair’, this was me not measuring up and this was only one of many many opportunities to follow.
Disappointment and frustration creates grit and perseverance.
Failing to see the bigger picture.
Your son is dreaming of the pilot lifestyle not thinking about the work as a pilot.
Start flying recreationally (gliders?) work on his education and try again later.