@ Keen while I love Matt Fraction and the Extremis is a good story idea I wouldn't recommend them to a 15 year old who's just getting into comics. In my humble opinion the stories you mentioned just don't have the right balance of character arcs and weight. Plus they tend to be stories that long-time readers would get more from then first-time readers.
Recently something has come out (which I noticed at my public library) that I think would better fit a young new reader: The Iron Man Omnibus by Kurt Busiek & Sean Chen.
This is THE "Jump On" book to get for anyone who wants to find out who Iron Man is as well as read excellent stories which involve The Golden Avenger in deep and interesting ways. It's not only jam-packed with arcs (see below) it also represents the fresh start Marvel gave their core heroes after the re-imagining of Heroes Reborn. So, essentially Tony has to come back from supposed death to rebuild his life and fortunes as well as get back to wearing the Red and Gold again.
This new beginning jumps right in with Shellhead facing-off against a collection of familiar opponents that will give the reader an understanding of the Armored Avenger's history and complications. Opponents include, but aren't limited to, the well-known and the obscure alike, with Whiplash, M.O.D.O.K., Fin Fang Foom, Count Nefaria and Ultimo rounding out the line-up. There’s also a brand-new villainous 'War Machine' Tony must uncover the mystery of and you-guessed-it Busiek couldn't resist working in The Mandarin.
We also have Happy Hogan and Pepper Potts supporting the cast while Stark somehow finds time to romance Rumiko Fujikawa. What's great about Kurt Busiek's work is that he always seems to keep the integrity of characters while giving us new spins on older characterizations and relationships. Something many of the newer stories tend to miss, Extremis for example, is Tony Stark's personality. Extremis not a bad story, far from it, but it doesn't have the intimacy with the characters that the award-winning Busiek can provide a reader.
Kurt Busiek explained in a interview, “Iron Man was the Marvel book I always wanted
to write, but it wasn’t because I was a huge fan of the series. There
are runs I like enormously, notably Archie Goodwin’s run on the
character, but what made me want to write Iron Man was that I saw so
much potential in the character, potential that I thought was only
partly-realized in the various runs of the past.”
That is why I would say this collection, more then any other, would be a great place for a new young reader to start. If it can't be found at the local library near you or at a shop for a good price you can check online.
This book collects a whooping amount of stories including cross-overs with other titles as well as the core IRON MAN Vol 3 series (#1-25). Some highlights: CAPTAIN AMERICA #8, AVENGERS #7, IRON MAN & CAPTAIN AMERICA ANNUAL, FANTASTIC FOUR #15, THOR #17, PETER PARKER: SPIDER-MAN #11 and IRON MAN: THE IRON AGE (Year One Style) mini-series.