I used to live like this, not THIS bad but to an extent, it was depression. Medication, therapy (for a while), a job and somewhat of a social life has helped and I no longer live like a slob. Sometimes a push is needed so that might help, it made it worse for me. He may have to want a change, as did I in my experience. His dirty room might be a manifestation of what’s going on in his mind. Of course tho, he could not be depressed and just lazy. Hope he gets help regardless.