I understand the worries over the age issue. It's not as you say, Jean, that the fact the Pevensies actors are older than their actual ages makes Ben's age somehow irrelevant. I haven't posted here in awhile, but there was actually quite a fuss on these boards about the age of Will and Anna in LWW, about how much older than the characters they were. As some have mentioned though, obviously it worked out well enough to suffice. I think Will and Anna both had enough naivety to act younger, and truth be told they weren't that much older than the characters they were supposed to be playing.
I think the issue at the heart of Ben's age is that Caspian's youth actually has a direct impact on the course of the story in "Prince Caspian" the book. Caspian is not simply looking for more troops, he's looking for leadership, someone to help lead him through a war he has no idea how to win. He's actually hoping that Susan's horn will summon Aslan himself to his aid, but seems just as willing to accept the Pevensies in his stead (which obviously ends up being the case).
I think what has to be resolved, now that we know who Caspian is being played by...is how the story will be adapted, because it will have to change. I do realize that Will will be approximately 3 years older than we saw him in LWW when filming PC, but the feeling the book gave you was that Caspian was basically in awe of the mere presence of Peter. Not only does Caspian convey this in the way he speaks and acts around Peter, but it's reinforced when Edmund goes into Miraz's camp to offer Miraz the chance to end the war via 1 on 1 combat with Peter.
The remark from Miraz's men (Lords Sopespian and Glozelle) who would later betray him was, "He that is walking between the Centaur and the Giant (referring to Edmund) has no look of surrender in his face, said Glozelle. Who can he be? It is not the boy Caspian. No indeed, said Sopespian. This is a fell warrior, I warrant you, wherever the rebels have got him from. He is (in your Lordship's private ear) a kinglier man than ever Miraz was."
Once they begin speaking with Miraz the Lords go on to mention, "For though I have never been called a coward, I must plainly say that to meet that young man (Edmund) in battle is more than my heart would serve me for. And if (as is likely) his brother, the High King, is more dangerous than he--why, on your life, my Lord King, have nothing to do with him."
As far as Prince Caspian goes, it's not my favorite of the books, so I guess I'm not as invested in this movie as some might be...but I definately see the issues that some people are having with his age. Basically everytime Caspian is mentioned it's as "boy" or "child", whereas Peter and Edmund are constantly portrayed as more mature, more regal, more intimidating. Makeup and props can make a difference, but I guess the issue everyone is having is how to make Peter and Edmund seem more assure, more savvy, more battle tested, more inspiring than Caspian when their is a pretty sizable age difference in the actors. Just in the quote above, can you picture how they're going to be able to portray Skandar as "kinglier than Miraz" to Caspian's "it's not the boy Caspian"? It's hard to fathom, which leads most to believe that they'll have to change the story.
Maybe it'll end up more as the Pevensie's acting as reinforcements rather than coming in and running the show as they did in the books. Heck, maybe they'll even change it and end up fighting Caspian against Miraz instead of Peter.
I think his age/looks will do him just fine in VODT, which I think could be the best screen adaptation of the series (though it's not my favorite book, if the effects are done well the movie would be amazing). I wasn't expecting much from this movie (since it's not one of my favorite stories), though I am hoping for a very good Reepicheep (both physically and the voice). I expect even more fighting scenes in this movie in comparison with LWW (since LWW the book really only had about 2 paragraphs about a fight which ended up a huge dramatic war sequence in the movie, whereas Prince Caspian the book spends significantly more time in describing fighting sequences).
I guess that's about all I have to say about Prince Caspian. The age does matter but it's not as if they haven't read the book, just means they'll haveta change the story to fit the characters they've cast. In the end I expect a better movie than LWW, simply because they learned alot in making the first movie. The special effects/animated characters will only get better since they're building off what they've done before. They should have more money to invest into this movie than LWW since LWW made so much money for them, and since they need to maintain interest in the series as they plan to finish all 7 movies. Who knows, it may even surprise me (and probably will).
