My mental images of each character varies from time to time. As my interpretations and perceptions ebb and flow, so does my understanding of their physique, personality, posture, etc.
Peter has always stumped me. He states he ran away the day he was born, and we are told by Barrie that he still has all his first teeth, but I don't imagine a very young boy as Peter. For me, Pan invokes an image of wildness - my Peter is savage, arrogant, deceptive, and eccentric. His hair is wild, his eyes are bright, and he constantly holds the air about him. He is savage, wild, free, and dangerous. He regards the world with a crooked smile, knowing nothing of the souls of others.
I'm quite sensitive about James, and so my understanding of him shifts even more rapidly than Pan or the others. There exists a difference between James and Hook for me. James Hook, as a person, is conflicted within. He is melancholy and proud, sinister and gentile, sensitive and enigmatic - he is a pirate and a gentleman, and it shows. Proud and aggressive, Hook appears as a strong man, tall, fit, and rough. James, on the other hand, is the gentleman, appearing sensitive, groomed, and thoughtful. Dark and brooding, James Hook is marked for death and the knowledge of his coming Fate has affected his mood and so outward appearance. He appears sickly, pale. And yet, his proud nature keeps him moving, and he readies himself for each day as if it is to be his last.