My guess is that it is ignorance and some of the same ignorant people look at the age of someone and think a younger person will somehow represent younger people better in some undefined way.

I’ve heard the low-wattage types (we probably all have) that looked at Biden and donnie and wrote them off as more or less the same because they are both “old white guys”. So they either didn’t vote, or voted third party…I bet these same types see Vance and think he is somehow a good choice for younger voters…