On this page about Principal boy:
In pantomime, the principal boy role is the young male protagonist of the play, traditionally played by a young actress in boy's clothes.
a number of conventions, which include: The leading male character (the "principal boy") is played...
prepubescent boys, because in some regards a woman has a closer resemblance to a boy than a man. The role of Peter Pan, for example, is traditionally played by a woman. The tradition of the principal boy in.... In the time of William Shakespeare, women's roles were played by men or boys, though there is some...