Peter Pan presumably decided he never wanted to grow up before he made it to Neverland. He was once a mortal boy with parents. He left these parents at an undisclosed age and made his way to Neverland. It is stated that he did once go back to see them, but saw there was a baby boy in his place. Assuming his parents did not want him, he returned to his life as an immortal adventurer.
Of Peter Pan's appearance and age, there are only hints. He is a beautiful boy, which could mean just about anything in regard to his complexion, hair color, etc. He dresses in leaves and sap, though Barrie puts it far more romantically than that. Well, he also mentions "skeleton leaves," which I do not understand, so I could have it all wrong. Nonetheless, he wears leaves in many adaptations.
The character is inspired by Barrie's own mother's memories of his brother, who died just before he turned 14. However, Peter Pan is clearly not as old as J.M. Barrie's brother. He states that he still has all of his baby teeth. According to the American Dental Association, permanent teeth begin to erupt around 6-7 years of age. Whether this is the age that Barrie intended or not, this is the age implied by the statement. Therefore, we can place him at a quite young age, which is a mite disturbing when you consider various actions made by the boy.
Peter Pan has several skills that even the Lost Boys do not possess or possess to a lesser degree. Firstly, he does not age, as I have mentioned. Secondly, his imagination is so powerful that he is able to think things into existence in Neverland. Thirdly, he can fly with the help of lovely thoughts and fairy dust, provided by his sidekick Tinker Bell. (The Lost Boys and the Darlings can also fly, but Peter Pan is especially good at it.) Lastly, he is a very skilled swordsman. He is so skilled that he is able to fight adult pirates, often even winning battles and memorably taking Captain Hook's hand.
While Peter Pan's personality is attractive in its nearly fearless and adventurous aspects, it leaves much to be desired in other areas. He is quick to come to the aid of friends, as evidenced by his rescue of Tiger Lily. However, he is also known to abandon his friends in their times of need. When the Lost Boys grow older, Peter "thins them out," which has been taken to mean exiling them or killing them. There is a theory that they become pirates, but this does not pan out, so to speak. Peter will switch sides in the middle of a sword fight with the pirates for fun, presumably injuring or even killing his usual comrades. As far as his smugness is concerned, that can be summed up by his proclamation, "Oh, the cleverness of me." after Wendy helps him reattach the shadow that he misplaced. He is also remarkably forgetful, which seems to be a result of his unending youth.
Regardless of Peter's characteristics, he is loved and/or respected by his many friends. When the Darlings are introduced to the Lost Boys, there are six, though there have been untold numbers before them. The Indians seem to have a peace with him and even the mean mermaids have a spot for Peter. Tinker Bell seems to be quite in love with him and maybe Wendy too. His only enemies are the pirates and maybe the Lost Boys that he maybe killed along the way, but you will not even see that on the Peter Pan Wikipedia page. It's clearly a delicate subject.