Interesting idea, Yannis.
I haven't taken the time to read through the entire thread yet but the title on the homepage jumped at me -- I grew up in a house where market talk dominated virtually evey discussion.
My father, eldest brother and uncle being heavily involved in the securities industry I could hardly escape discovering the markets and thus developed my own interest in them, although it's difficult to say how much of this was a conscious choice and how much of it happened because of some 'hidden desire' to 'live up to' my (what I might have thought were) family's expectations.
At about 15/16 I began to be taught in a more formal, systematic manner about the markets. Personally, I loved it. I was a bookish kind of kid (still am!) and being asked to sit down and study the various concepts being described jibed well with me. Perhaps had my situation been different, it might not have worked so well. As it is, though, looking back, I'm very pleased with the way the whole thing went and really only have positive comments about the experience.
Is your son actually interested in learning about trading and the markets? Interests can be developed, to be sure, but perhaps at his age it would be best if this interest were already there, to some extent.
I did read the first few posts, warning of the dangers of teaching a 14 year old to trade. Overblown, I think. Teaching a 14 yr old to trade doesn't mean sitting him down for lecture after boring lecture and forcing him to pour over chart after chart for hours on end (certainly not handing thousands of real money for him to be exposed to the rigors of real trading); the teaching can take place slowly, over time. If at some stage your son decides that he's really not interested I can't see how any real harm would have been done.
It's probably already been suggested, but, at the same time as you introduce some general concepts, let him read Reminiscences. I think it's an engrossing story -- even for non-traders -- and will quite likely keep his interest high and thus add to any 'formal' lessons you try and teach him.
Good luck!