In the US its common for people (non-Catholics) to raise other people's kids (not condemning that per se). But the reasons for this is that people lay down with each other and start a family out of wedlock and then later don't like that person and trade them in for someone else and the cycle continues. Seems to be a trend among my generation here.
I never saw that once living abroad. Never knew someone raising someone else's kids (step-dads etc).
So maybe it's not that people shouldn't marry. It's definitely a cultural thing. My wife was a 35 y/o virgin living with her parents her whole life when we got married (that's how they do it in other countries). You'd be lucky (blessed) to find one (a non-Catholic again) at 18 of such disposition here in the U.S., from what I understand.
You'll find a few in the US, but they won't be American and probably not Catholic, either. They will be the adult daughters of Asians, Arabs, Indians, Africans for whom culture dictates an unmarried daughter lives with her parents.
Personally, I'm glad I never married or had children. I see what has happened to those of my age group, 55-65, all divorced, raising their grandkids of assorted unmarried children with multiple partners, all have lost the Faith, most follow no religion whatsoever, a chaotic, charityless mess. I moved out at 18, female or not, it was expected. Wanted when young to be a teaching or medical sister, but by then, the convents were empty, just nuns in pantsuits with bad hair, into occultish trash or silly political causes. I'm nearly 60, too late for sisterhood, fair health, working long hours to survive. I'll be satisfied to die at any time, so long as I'm in a state of grace.