Living with late teens, early 20s children

[SilverDoublet]

My kids are still pre teenagers, just about, but in our area the cost of renting a flat or house share is insane, so we're looking at them living with us til they are mid 20s, I would think. Those of you that have teenagers/ young adults, do you allow them to have gfs/bfs stay over? What age would you allow them to do that? Do you allow it every weekend or on a regular basis? What about casual relationships...

Any insights or opinions welcome!
Thanks.

Fuck no. I’m not running a knocking shop! If sex happens I expect it to be secretive, quiet and hopefully not in my house! It’s probably much more exciting like that anyway. Who would want patent sanctioned sex??
Also, I will do my utmost to make sure no adult children are living with me past age 21. At the latest. Sure, they can come back to stay , but solidly living with me until the age of 25? No. I really hope not anyway! Wouldn’t that be kind of a failure to launch??