knb, does your nephew know about lesswrong, rationality and the Singularity? I guess I would have enjoyed reading such a website when I was a teenager.
When it comes to a physical book, Engines of Creation by Drexler can be a good way to introduce him to nanotechnology and what science can make happen. (I know that nanotech is far less important that FAI, but I think it is more "visual" : you can imagine those nanobots manufacturing stuff or curing diseases, while you cannot imagine a hard takeoff).
Teenagers need dream.
My sister and brother-in-law are both semi-religious theists, so I'm a bit reluctant to introduce him to anything as hardcore-atheist as Less Wrong, at least right now. Going through that huge theist-to-atheist identity transition can be really traumatic. I think it would be better if he was a bit older before he had confront those ideas.
I was 16 before I really allowed myself to accept that I didn't believe in God, and that was still a major crisis for me. If he starts getting into hardcore rationality material this early, I'm afraid it could force a choice between rationality and wishful thinking that he may not be ready to make.
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