Such an interesting thread. Loads of good suggestions. I add another vote for Bill Bryson. Wonderful, underrated writer. Just because a writer is popular, that doesn't mean they're mediocre. The Sherlock Holmes books, for example, are excellent, and yet they've always been very popular. P G Wodehouse is another example – a superb stylist, and such a master of language that people have compared him to Shakespeare, but also very popular. How about something by Stephen Fry? He's always SO interesting, so learned, and yet never dry or pompous.
Being a male, he might be put off, but how about Jane Austen? Martin Amis said that until he was 14 or 15 he did nothing but smoke and read comics. Then someone gave him Pride and Prejudice and that was it. His life changed forever. Books like P&P or David Copperfield or Sons and Lovers have lasted for a reason.
Just a thought, but different authors offer different things. If you want him to cultivate a love of language, then I'd recommend Anthony Burgess, Evelyn Waugh, P. G. Wodehouse, Virginia Woolf, etc. Their books read almost like poetry. Burgess especially is extraordinary (A Clockwork Orange would be quite a cool book for a teenager boy – maybe he could watch the film first).
Then you get writers who are just wonderful storytellers (Dickens, Jane Austen, H G Wells etc), or great at dialogue (Oscar Wilde especially), or have a knack for thrilling ideas (Ian McEwan, Aldous Huxley, Douglas Adams, Primo Levi).
Ah...just thought of a great book for a young person getting back into reading: Siddhartha by Herman Hesse. Short, simple, mystical and beautiful. Robert Graves' I Claudius? Again, he could watch the (superb) TV series.