Politically, they're sure acting like it. If you take the Catalist data (linked to in previous posts) and look at the contributions various demographic groups made to the Democrats' improved performance (national-level) relative to both 2016 and 2014, you find these voters looming very large indeed.
Relative to 2016, whites under 45 can more than account for the entirety of Democrats' improved performance. Relative to 2014, these voters account for around 60 percent of the Democrats' improvement between the two midterms (the rest in nonwhite voters, particularly blacks).
There is no demographic force more powerful than generational replacement. The effects on politics can be very large and I think we are starting to see that.