I will never kick them out. They can stay for as long as they want.
I moved out at 22 when I built my own house. Living at home meant I could save and do that.
Turns out I hated living in the suburbs and after 3 years I moved home to sacs up go build a house in the country (my parents live on 10 acres). I realised I wanted to buy their house so now I pay off this house interest free while sharing with them.
We added an extension so we could have our own area. It's the perfect arrangement for us as they watch the girls when I'm on night shift.