There was actually some news recently that these polls might actually be wrong here: apparently there's a large amount of people lying that they're Hispanic/young in online polls. This was discovered both because: 1. The "20% of youth are Holocaust deniers!" Poll that made the waves wasn't reproducible and 2. There's some BIG inconsistencies being found in many polls too, like some polls somehow managing to have a cohort of Hispanics that are 20% nuclear submarine engineers.
Basically, we might have a vicious cycle making polls wildly inaccurate here: youth (and Hispanics?) are harder to poll -> pollsters value the data more vs other demographics-> people lie to obtain the rewards being offered to get this data -> youth/Hispanics become harder to poll.
Polls usually can handle some "lizard man's constant", but everything falls apart if there's significant lying.