>Through her, I know quite a lot about fertility issues.

I empathize with your sister, but I think it's wrong to generalize a single data point over the population. On a broad level, birth rates in the US from 25-29 are at 104.3, whereas 30-34 is at 101.5[1]. This is a change, but far less in comparison to the dropoff at 35-39, where birth rates fall off a cliff to 51.8.

If we take the article's premise at face value (college educated women in current times typically give birth at ~30 years old, vs non-college educated women at ~23), it would appear that the birth rate differences are negligible.

[1]: https://data.cdc.gov/NCHS/NCHS-Birth-Rates-for-Females-by-Ag...