How so? Looking at this Pew data[1] on median household income in 2017 dollars, which appears pretty comprehensive, if you have a college degree, millennials are doing slightly worse than Gen X, but better than all generations before that looking at the same age range.

Even those with "some college" millennials are slightly worse off, but within 5%.

It's those with only a high school degree that have seen a significant hit.

[1]https://www.pewsocialtrends.org/essay/millennial-life-how-yo...