Even without YA-Adult conversions, the YA clothing seems to appear on the adult section as well. My hoods are pre-modern or historical so I prefer custom clothing rather than defaults in my game. I found hiders for almost everything but is there a hack that hide YA clothing, especially the ones for adult? (or else the student CAS might be empty... )

If it's custom you are probably going to have to remove the coding for the YA bit from each recolour. I'm not aware of something that does that automatically though there might be something. You might be able to batch change it in SimPE.

I have a hack that allows AF and AM clothes to show up for Elders. It could be that you have a Mod that makes YA clothes show up in the Adult section. I'm not sure, that's what it could be.

Maxon
No, I'm not talking about custom clothes that appear on both YA and Adult, but the one that hide maxi defaults such as these:
http://www.modthesims.info/download.php?t=540540

I don't remember where I got them but they're called HideClothesSP/XP and which pack it is. I've 15 packages of them but can't find anything that remove the YA defaults or at least most of them. I'm consider using defaults that change them to historical styles but I find the clothes overwrite sometimes which other clothes, creating chattered outfits (the type that try use two meshes at the same time) and therefor prefer non-defaults and hiding the maxi ones.

Without looking at the files, I'd guess they enabled the YA clothes for adults as well as hiding the hobby clothes. If I get time, I'll have a look at it tomorrow.

Well, I looked at CAS adult screen when buying clothes, it seems to be several random outfits from different XP/SP. Remember wrong and thought the adult section showed the outfits the premade YA sims using like Blossom Moonbeam's crop top/maxi skirt outfit, but it wasn't there.

Weird, I thought I had the ones that hides the kimonos, apron from base game.

Blurry but attached a picture of all maxi outfits the hiders didn't take. The only ones that suppose be there are the military outfits which is unlocked versions, but doesn't have custom icon for some reasons.

EDIT: Yep, the YA maxi clothes seems to be in the right category after all. Now I'm just wondering if it's possible to hide them consider they only appear in th CAS screens at Uni, but I don't create students...