Historically shared living was standard. You had multigenerational households and such too. It was not seen as humiliating, but as normal.

It has its issues and is definitely not ideal, but whether you accept these has less to do with age and more to do with culture and economics.

How do you start sharing multigenerational household when you're a foreigner hundreds kilometers away from any family? Culture and economics might mutually agree that you are obsolete and should eliminate yourself, would you comply?

Indefinitely, if you can't afford to live alone. It's obviously not something you'd want to do, but it's much better than being homeless.

I've shared a house with people in their 40s (or more) when I was in my 20s in London. I'm sure they would have preferred their own place, but it was much, much cheaper for them to share.

If someone in their 40s ends up or insist on living in shared accommodation in London, it's probably a hidden message from their own destiny.