My 15-year-old nephew is reading Stephen Fry's autobiography Moab is my Washpot, and loving it. At his age, I loved Roald Dahl's autobiography Boy.
I'd recommend the following for an intelligent young person just getting into reading:
George Orwell: Down and Out in Paris and London
Robert Graves: Goodbye to all That
H. G. Wells: Science Fiction stories
Jane Austen: Pride and Prejudice
Steinbeck: Of Mice and Men
Salinger: Catcher in the Rye
D. H. Lawrence: Sons and Lovers
J. G. Ballard: The Empire of the Sun
Also, try The Sherlock Holmes books, read by Stephen Fry. Wuthering Heights, Emma, The Picture of Dorian Gray and even Woolf's Orlando or Dickens' David Copperfield are all very readable. We underestimate young people.
You also want to encourage a love of language. Kipling is perfect for this. The Jungle Book and Just So stories on audiobook are great. P. G. Wodehouse is another writer whose language sparkles. Stephen Fry has recorded a lot of Wodehouse on audiobook.
If he has a sciency brain, then Bill Bryson's A Short History of Nearly Everything. Even though I'm very bad at science, this is my all-time favourite book.
Richard Dawkins Magic of Reality is aimed at younger readers.
Carl Sagan's Cosmos is wonderful. He might find it heavy going in places, but it's the perfect book for a young person.
And anything by Douglas Adams.