http://en.wikipedia.org/wiki/Peter_Pan_(1954_musical)
Further addressing the question of tradition, the wiki entry says this:Peter Pan is a musical adaptation of J. M. Barrie's 1904 play Peter Pan and Barrie's own novelization of it, Peter and Wendy. The music is mostly by Mark "Moose" Charlap, with additional music by Jule Styne, and most of the lyrics were written by Carolyn Leigh, with additional lyrics by Betty Comden and Adolph Green.
The original 1954 Broadway production, starring Mary Martin as Peter and Cyril Ritchard as Captain Hook, earned Tony Awards for both stars. It was followed by NBC telecasts of it in 1955, 1956, and 1960 with the same stars, plus several rebroadcasts of the 1960 telecast. The show has enjoyed several revivals onstage.
So you see, even the original 1905 play by Barrie featured a woman as Peter as a kind of derivative of the pantomime tradition where the role of the Dame is always played by a man.Several productions of Peter Pan were staged early in the 20th century, starting on Broadway in 1905 with a production starring Maude Adams. In a nod to the original play, and the pantomime tradition it derives from, the title role of Peter Pan in the musical is usually played by a woman, including Mary Martin, Sandy Duncan and Cathy Rigby, among others.[1]
While we think it would be a great role for a Billy to play (and it would!) the revival of the Broadway production is bowing to the venerable tradition of the show in casting a woman as Peter.
I might add that Peter Pan is a popular production for community theatre, and there have been a couple of stagings of it locally this year in which Peter, as expected, was played by a woman or a girl.