We [...] find that for the generation coming of age in the 2000s, student loans delay fertility for women, particularly at very high levels of debt. Home mortgages and credit card debt, in contrast, appear to be precursors to parenthood. These results indicate that different forms of debt have different implications for early adulthood transitions: whereas consumer loans or home mortgages immediately increase access to consumption goods, there is often a significant delay between the accrual and realization of benefits for student loans.
And from 2019, Married with Children? The Role of Student Loan Debt:
Prevalence of student borrowing by age 25 was at 45% in 2016 (compared to 25% in 2004) and their findings further indicate a dramatic shift toward student loan debt as the primary source of debt for young adults (whereas young Americans have shown declines in mortgage debt, auto loans, and other consumer debt)
When I was in high school, college wasn't seen as something only the elite did, it was something everyone was expected to do. I can only speak to my experience, but as someone who grew up squarely in the middle class, I knew and all my peers knew from a young age that we were going to go to college. We called it "higher education" but it was really just the last 4 years of school.