An excellent anime with a compelling story that is well written, I would recommend Code Geass to any serious anime lover. It fantastically combines the “Humongous Mecha” genre with the supernatural in the form of Geass, and adds to it an epic cast of characters, and a plot that hinges, not only on action, but massive amounts of thought provoking elements that get the viewer thinking. It even contributes various philosophical questions into the mix. The story focuses, not only on the protagonist, Lelouch, but also on Suzaku and many other characters that are central to the plot. Personally I do think that the show provides positive role models with a positive message, though your mileage may vary on that.
As far as the content goes, due to violence, strong language (especially in the subbed version), some nudity, and some use of alcohol and other drugs (notably refrain), as well as the complicated nature of the show, it is clearly aimed for a higher age bracket, most ideally young adults. However, I see no reason why a 14-year-old can’t watch it, given that he or she is mature enough. When it comes to shows like this, I would say it’s like sex; you are ready to watch it whenever you feel mature enough, and ready to face the consequences. Therefore, I say pause at 14, and definitely ok for 16-17 and up.
My only major complaint is that there were too many product placements. If there ever was a censored version, I would half-expect Kallen’s nipples in the nude scenes to be covered by Pizza Hut logos, instead of censor bars.