Posted by: @courtenay

That whole scenario is crucial for setting up the rest of the story — they could actually open the series/film of PC with it, before cutting to the opening of the Pevensies' story at the railway station — and Caspian really needs to be "only a very little boy" (to quote the book) at the time for it to make sense, especially to capture his wide-eyed wonder at these marvellous stories of Old Narnia, and then his horror when he discovers his nurse has been sent away because of what he said to Miraz. That, in fact, is one thing the Focus on the Family radio play version of PC messes up — they use the same voice actor for Caspian throughout, so at his first "appearance", when he starts talking to his uncle about "the Old Days" and gets into trouble for it, he has the already deepish voice of a teenager. It just sounds completely wrong for that scene.

I didn’t think he was that much older for the rest of the book for a while, lol. There was a brief mention of a time skip but it was kind of easy to overlook because it was vague about how much time. I read something when the PC film was released that a lot of readers apparently interpreted Caspian as a child, with the director having specifically noted a brief mention of him being about Peter’s age. (This comes much later in the book, after all the flashback stuff).

Posted by: @the-mad-poet

  I lean more towards one person to play Caspian in PC, VDT, and the end of SC. The idea of having a 20 year-old sounds pretty good (actually Ben Barnes was 20 years old in Walden's PC), but he should still look like a 'boy-king' in VDT.

In fact Ben was 26 in 2007 when he played Prince Caspian (released 2008).  (I just reread the thread and noticed this - twice the book age)  

By 2009, acting King Caspian for the 2010 release, he was 28.