There are the books you like, and the books you can recommend, and the books around which you can muster arguments. And then there are the books from which you can get no aesthetic distance at all. Often they’re books about childhood, or about something or somewhere you knew as a child. They can also be books about books. Among Others by Jo Walton, is one such book for me, and not for me alone: last week it picked up the British Fantasy Award, having already won the Nebula and the Hugo for the year's best science fiction novel. The two awards together describe the state of SF (one’s voted on by working authors, the other by fans); when the same book wins both, it’s a recommendation, and it says something about the state of the genre.

And yet Among Others is not science fiction at all, if you judge by its plot. Morwenna Phelps, from the Welsh Valleys, aged 15, goes to Arlinghurst, a supposedly top-flight, certainly snobbish English girls’ school; Mori can't stop thinking about her dead twin sister, and about her tyrannical mother, who has faerie powers – the previous summer Mori ran away to escape her. (Walton gradually makes clear that the faeries are real.) Written as Mori's diary, with terse events and seriocomic asides (‘Why aren't I like other people?’) Among Others follows her first year at school, competing with girls, making friends with boys, coming to feel at home in the town library, making sense of her grief, and defeating her mother by literally finding magic in books.

All that's done well, but it's been done before (for example, by Diana Wynne-Jones). Morwenna’s – which is to say Walton’s – distinction lies in what she reads: stacks and stacks of fantasy and science fiction, starting with Kurt Vonnegut, J.R.R. Tolkien and Ursula LeGuin (whose works she brought along when she ran away) and proceeding through the genres’ highlights c.1979: Roger Zelazny, Samuel Delany, Christopher Priest. Mori seems well on her way to becoming a writer; indeed, she may be on her way to becoming Walton, who also grew up in the Welsh valleys, also walks with a cane, and who would have been 15 in 1979-80, when Among Others takes place. ‘When I grow up,’ Mori says early on, ‘I would like to write something that someone could read sitting on a bench all day that isn’t all that warm and they could sit reading it and totally forget where they were or what time it was so that they were more inside the book than inside their own head. I’d like to write like Delany or Heinlein or LeGuin.’

Morwenna has two restrictive worlds from which she’d like to escape: the school’s and her mother’s, the world of the faerie folk whose nature-magic can tie you, for good and ill, to the land. Against both school and home, the past and the present, Mori sets the promise of the future, both her own immediate future and the imagined futures of SF.

If you grew up reading Delany, Heinlein or LeGuin, those futures have now become part of your own past. Mori’s musings, and her well-catalogued growth as a reader, speak to the power of childhood reading in general, though they also say what SF in particular can do. The promise of wonder and strangeness comes together, in SF, with the promise of logical laws. And the promise that the future will not be the present, that things can be different, which Fredric Jameson (among others) sees as the heart of SF’s political virtue, turns for Morwenna into the friendlier and perhaps more reasonable promise that her future will not be her present.

Like thousands of young SF readers before her – including me, exchanging endless dollar bills for endless paperbacks at Second Story Books on P Street in Washington DC – Mori has been learning about real adult life through science fiction, and so she's not sure what's real and what's made up. (Mori’s antipathy to realist fiction in general, and to Dickens in particular, is a running joke: she does like T.S. Eliot and the Aeneid.) When she reads Zelazny’s Doorways in the Sand, set in an American university, she believes his wacky inventions are real features of US education. And when she gets a boyfriend, near the end, she's baffled by the distances between the polyamory and free love in Heinlein and the complexities of her own experiences. But the same science fiction that may steer her wrong also saves her, not just by giving her ways to battle her mother, but by letting her put the bad things that happen to her into perspective.

Among Others shows, with irony and glee, what it’s like to grow up with SF as your guide. And yet its scenarios end up sadly familiar: it’s not a work of science fiction so much as a work about science fiction, an almost realistic (except for the faerie parts) novel about what other novels do. It is not so much a telescope as a mirror; in it, you may see a flattering and vulnerable version of your younger self. Publishing observers have been warning since the advent of computer gaming, if not since Star Wars, that science fiction in print faces an ageing audience and a demographic decline. If Among Others is (and it may be) the best SF novel of last year, that distinction may hide a warning: science fiction, and its readers, may now take less interest in farflung futures than in our own past.