At Whatever, John Scalzi notes the very good reasons why the young of today aren't reading the classics of old science fiction. (They are young, and of today.)
The surprise to me is not that today’s kids have their own set of favorite authors, in genre and out of it; the surprise to me is honestly that anyone else is surprised by this. As a practical matter, classic science fiction isn’t selling where today’s kids are buying (or where they are being bought for), namely, in the YA section of the book store. See for yourself: Walk into your local bookstore, head to the YA racks and try to find a science fiction or fantasy-themed book that more than fifteen years old. It’ll be a rough assignment. YA has a high audience turnover rate — kids keep aging out of the demo, don’t you know — and the new kids want their own books. The older books you’ll see tend to be a) ones assigned by schools, b) ones that had movies made from them.
Mind you, generally speaking, book stores stock newer books anyway; book stores, like other entertainment venues, rely on novelty (which in our line of work is called “front list”) to get people through the doors. If you’re doing well as an author, some of your backlist is on the shelf, too. But the shelf in a physical bookstore is only so long. These days, being someone who has been in a lot of bookstores recently, I note the shelf in science fiction and fantasy is mostly skewed to living, working authors, most notably their last couple of books. Some classic (i.e., now dead) authors are there but usually represented by two or three books rather than an extensive backlist.
Which is as it should be. All love to Heinlein, Clarke, Asimov, et al., but they’re dead now. They don’t need the money from readers; living authors do. Moreover, Heinlein, Clarke, Asimov, et al have been dead on average two to three decades and their best known work is half a century old. No matter how brilliant they were or how foundational they were to the genre, they’re going to be dated. None of the futures of Heinlein , as just one example, resemble a future that begins from today; they branch off from the 50s or 60s. Readers (in general) don’t want to have to go backwards a half century in order to move forward again.
Certainly you can’t expect new readers to the genre, including young readers, to backshift several decades — or, well, you can, but it would have the same effect as suggesting to a teenager today that if they want to see a movie about people their age, they should watch The Blackboard Jungle. Sure, it’s fine movie, and an important one. It’s just not especially relevant to the teenager of today. It wasn’t made for them, in any event. It was made for their grandparents.