Well I think you have to look at the reasons for why they are living in this state. Sometimes, it's because they refuse to allow anyone to come in and clean it up for them. Many old people have a fierce independence and wildly resent any attempt to interfere with that by unsolicited help from a family member or a charity or a government agent. In fact, when I think about it every single one of the old people I've come across living in these conditions, has been doing so precisely because they insist on it.
I have a friend who had an elderly relative living in this kind of squalor. When she visited her and started organising her stuff and asking her what could be binned and what better organised, offering her Dh's services to put up shelves etc., the old woman started screaming at her to get out of her house and leave her alone. She then phoned up her mum, crying down the phone about how my friend had upset all her stuff, interfered with her privacy, etc,
You've got to be very careful about telling older people how they can live. All of us could see that my friend technically was right, the house should have been cleaned up, but actually she was wrong, because it wasn't her house, it wasn't her problem, and she simply didn't have the right to be so officious as to take it upon herself to "organise" this woman.
I'm not saying it's always the case that OP's prevent anyone from helping them, but I used ot work for an OP charity and have just realised that I hadn't come across one old person who lived in this manner, who said "I'd really like someone to sort this out for me". Every single one of them refused offers of help.