This story takes place a year after the events in the Lion, Witch, and the Wardrobe. Peter, Susan, Edmund, and Lucy as summoned to Narnia by Caspian who blows Susan’s magical horn. Readers will remember that Susan was wearing the horn on their last day in Narnia. The horn had been lost for ages. Their job was to help Prince Caspian reclaim his throne.
After the Pevensie children returned to our world, Narnia was conquered by a race of men known as Telmarines. These men feared the mythical creatures of Narnia as well as the sea. As a result, Narnians went into hiding. The woods grew till Cair Paravel was cut off from the rest of Narnia. Approximately 1300 years have passed when they returned.
Prince Caspian is the crown prince of Narnia. His uncle Miraz is his Regent as his father, Caspian the IX was dead. Prince Caspian’s nurse taught him about Old Narnia. However, she was sent away when Caspian inadvertently told his uncle of the stories. At this point Caspian was taught the skills necessary to become a warrior. His tutor was Doctor Cornelius, who was part dwarf. Dr. Cornelius also taught him about old Narnia. However, Caspian was now smart enough to realize that he should keep his lessons quiet. Several years past, before Miraz was able to produce an heir. At this point, Caspian’s life was in danger. So Dr. Cornelius sent him from the castle one night with Susan’s horn. During his flight, Caspian fell off his horse. He woke up in the company of Trufflehunter, Trumpkin, Nikabrik- Old Narnians. The trio took Caspian around with them to meet all the true inhabitants of Narnia. After meet Glenstorm, the Centaur, they realize that the time of war is upon Narnia- and Caspian must lead them. In their counsel of war, they decide to use the horn. They believe (Dr. Cornelius has joined them at this point) that the horn will summon the Pevensie four. However, Dr. Cornelius believes that the four will be summoned to their castle at Cair Paravel. Trumpkin is dispatched to bring them back. He is captured along the way, but the four rescue him.
They reach Caspian before the battle begins. But they have to fight off a werewolf and hag Nikabrik has brought into their counsel in order to resurrect the White Witch. Peter and Edmund stop that but Caspian is injured. In order to give the weary Narnia troops some time to rest, Peter decides to challenge Miraz to personal combat. Meanwhile Lucy and Susan, who are with Aslan, go to wake up Old Narnia. During the combat, Miraz is killed by his own treacherous men, and the battle starts in ernest. Alsan, Lucy, Susan, and the rest of the Old Narnians come to the rescue. Caspian is made the High King of Narnia. Peter and Susan reveal that they will not be coming back to Narnia as they are too old.
Now the interesting question is how is Caspian. The only reason I bring it up is because Ben Barnes, the character who plays Caspian in the movie is older than the little boy who played Caspian in the BBC version. The clue can be found in a review of the process by which a boy became a knight. There is speculation that Caspian was 13 when the Pevensies returned. I’m thinking he may have been a bit older. A boy began his training as a knight when he was 8 years old. As we see in the beginning of his story, Caspian’s made some dumb comments to his uncle. The type of comments that a small child would make. Soon after his begins his training. The book says some years past before Queen Prunaprismia has her baby. During this time he we are told he learned heraldry, archery as well as sword fighting. Now from what I’ve read, although swordsmanship was taught to pages, the training did not begin for real until they reached the squire level which is when they would have received their first set of armor. This was around 15 or 16 years of age. This would have put him closer to Peter’s age. In fact in chapter entitled Sorcery and Sudden Vengeance, Peter notes that Caspian is about his own age. We know from the Voyage of the Dawn Treader that Peter was taking exams and being tutored by Professor Kirk. I believe in the English school system (Litlove correct me if I’m wrong) there is a set of exams taken when students are around 17 years of age. So Peter was probably 17 in Voyage of the Dawn Treader which would have made him 16 in Prince Caspian. We also know from this same book that a year had passed on Earth since Prince Caspian while 3 years passed in Narnia. We know that at the end of Voyage of the Dawn Treader, Caspian marries Ramandu’s daughter prior to returning to Narnia. Which would make more sense if Caspian was 18 or 19 years old rather than sixteen. In addition, we are told by Caspian that he had waged a major battle against the giants a year before his voyage. I think that’s a bit much for a 15 year old to accomplish. So no, I’m fairly confident that Caspian was probably 15 or 16 when Prince Caspian takes place.