This was very common in my extended family in rural North Carolina. Most of my cousins didn't attend college, partnered up quickly, and started families. Not always in that precise order . . .

Honestly, I think for them it just wasn't that odd in their community. I grew up in a more suburban area and the baby boom was definitely a few years later comparatively speaking.

I have several aunts and uncles who are great-grandparents and in the 60-70 year old range.