Johnny Doughboy (1942)

An arrogant young actress doesn't want to play "young" parts anymore, and runs off. The studio replaces her with the president of her fan club, who just happens to be a lookalike. Meanwhile, some other former child actors, trying to put on a show for the GIs, will be able to do it only if they can get the young actress to be in it, so they set out to persuade her to be in their show--not knowing that she's isn't who they think she is.