Correcting a mistake about age...
Contrary to what a few of the comments here suggest, Bruni (VIRGINIA CHRISTINE) and Oley (HARRY MORGAN) were not playing Kristina's (OLIVIA DE HAVILLAND) parents. They were her close friends, not her parents.
Someone noticed that they were all about the same age--but that doesn't matter since they weren't supposed to be her parents. Where that impression came from, I don't know.
As for the ages in general, I agree that almost the whole cast was too old for their roles--especially Mitchum and Sinatra as medical students when they were clearly nearing their forties.