My dad has made it clear that as old age comes, he has no intention of ever living with me for any reason. We have an awesome relationship but he wouldn’t want to either feel like he’s mooching or to feel like he can’t call the shots in his own home. He didn’t have to explain the feeling, I just know how he is. “Fish and relatives stink after three days,” and all that. I lived in Europe for a while and found out my friend’s grandfather lived with them, in a separate room where he just stayed for 20 hours a day. I could see the advantages immediately, the space efficiency and nearness to a family who cares, but my dad would rather die than live that way.
My kid is a preteen. He can stay with us as long as he wants to be provided he is doing something productive with his life and working toward self-sufficiency. I only care about that really because it is good to have professional and personal goals and I want him to be able to take care of himself after I die. I would never make him move out because he is a certain age. I am from the USA and I told my kids many times to get out at 18, but they both knew I didn’t mean it and just laughed at me. My son did move out at 19, his choice, my daughter is still living with me at age 25 and getting her master degree.