That’s definitely a known problem, but to even start fixing it the DNC has to start promoting progressive policies that actually look forward to addressing the issues of the future rather than trying to bring us back to the “normal” of 1992. Instead, the Dem establishment continues to try to attract middle-aged “independent centrist” and “undecided” voters (AKA morons who are prone to vote GOP) to try to make its margins.
Uncle Joe’s appointments and choices of advisors so far don’t offer a whole lot of hope for change in this regard. To be sure they’re more competent and serious about public service than Biff’s coterie (jumping a very low bar), but I’m seeing a lot of the same old neoliberal-lite, tough-on-immigrants, and oil-and-fracking-friendly Dems who have been around since Clinton [topic for discussing that is here]
tl;dr – give young people candidates and policies that are focused on making real changes (rather than the hopey kind) and the Dems might start making a dent in the problem.