except that's not what this "intervention" is going to be about though, is it? He doesn't look awful; most of his clothes fit and could work in slightly modified combinations. Noone is going to be able to give magic bullet that will suddenly make him look amazing.
it will consist maybe 1% of people saying "those clothes don't quite go together, but you're getting there"
and the remaining 99% will be people telling him to completely change his taste, stop buying X brand, stop shopping at X store etc.
The reality is that he's probably slightly new to this and simply hasn't quite built up enough of a wardrobe to be able to make the optimal choices with what he wears.
The only way that's going to change is for him to organically gain more clothes and experience, not through any "intervention".