Two of my boys have already left home, although very sad for me at the time ( still is if I'm to be honest)I know it's a natural progression.
I would never ask them to leave, well maybe if they were the entitled no hoping type, but my door is always open for any returns lol
My last son will be joining the army and leaving early next year,it's really hard to let go, to me he is still a baby but I'm confident he will do well.
So no I would never have a magic age where they were expected to leave and the locks changed lol
It's very confronting when your children start to leave home!