I was born into a blue collar, hard working family in the 60s. Kids stayed at home until they married. My grandparents were legal immigrants from Italy and Ireland. Families lived on the same street or neighborhood in South Philly.
That was pretty much the model in my own extended family, but most of my siblings, cousins, and I, were out of the house and married by the age of 21. Even those who didn't marry right away, were up and gone by at least the age of 22.