I may not have been entirely representative as a child, but really, many of my peers did the same thing: reading books for 8+ when aged 6, and for 12+ when aged 8-10. As a result, I'm rather sceptical about the upper part of the professed range for YA books. At 16 or more, one is plenty old enough to read normal adult literature, surely, and also old enough to feel that "YA" books are more for younger children (though they can still be fun, of course). Though if one counts The Catcher in the Rye or To Kill a Mockingbird as YA, which I personally wouldn't but one of the Wikipedia articles seems to, then yes, those are very much suitable for 16-year olds.