Well, my girls are 14 & just turned 18. I promise you they know who John Wayne, Katharine Hepburn, Grace Kelly, James Stewart and others are. My oldest took a summer course for fun called "The History of Motion Pictures" and just about every movie discussed in that class was in TGMR or in the final scene.
We regularly have family movie night and take turns picking out movies. After watching an rerun of Castle I said "wow! that's a lot like Rear Window"....that Saturday my oldest daughter went to the library and checked out Rear Window and Rebecca. So we had a Hitchcock double feature. Just because a movie is older doesn't mean the younger generation can't or won't appreciate it....they just have to be given the opportunity.