I was the youngest child in my family. As long as I could remember, on my birthday, Dad would announce "Only X more years, and you're outta here!", with X = 18 - My Age. On my eighteenth birthday, my bag was packed, and I was outta there!
I would not be surprised if he said that at my first birthday party. He certainly said it at every one from three to seventeen!
In retrospect, was he right? We didn't kick him out at 18, we did at 19, then he came back, left again, came back, etc until he learned his "date". It worked. We began to pack his bags and he got the message.
i told my 4 kids that "It's a law that you have to move out by 18". Started when my oldest was 9, now 15. My wife rolled her eyes but I told her that every serial killer on the television news "lived at home with mommy"... 'nuff said.
My wife has a similar comment. We homeschool the kids. Her mantra is "Two Thousand Seventeen!!!" That's when the last kid graduates.