TBH for me this wouldnt be a LTB situation, not quite yet.
I would tell him that he needs to go to the Dr and explain that he is having some issues with hoarding, and anything else that could be related in a mental sense. Hoarding can actually be part of OCD.
I have always, always had shit everywhere. Really struggle to throw things out, but then I also really struggle with my space needing to resemble clean, and to be clear of clutter to feel happy. What most people didnt realise was that I had two rooms of my house that were completely full to the brim with shit id collected and couldnt let go.
Every cupboard, every drawer, my car boot, everywhere I can store things, I do when Im not well.
When i had therapy, it got significantly better, maybe it could for him.
Something that I found particularly helpful was when I considered what people usually keep hold of, and how that actually aligned with my own collections of items, then I had to question why, and what I was gaining from keeping those items, and what would realistically happen if I didnt have them?
How were they making a positive impact on my life?
Even now, every few months I need to go around the house with a bin bag, I have to throw out items that we dont really "need" infact, I have to prepare my youngest sons clothes that hes outgrown, and all of the accessories from when he was a small baby for an NCT sale, because even though its out of sight, I KNOW that I have got a bit out of hand with not letting things ago in that respect.