Beguiling Masquerade by Carole Gift Page

When quiet graduate student Becky Chandler dresses up as an elderly woman to research her thesis, she finds herself more outgoing and talkative, especially with her newfound friend, Myrtle Watson. But when she meets Myrtle's grandson, Becky is stunned to learn it's Rand Cameron, her sociology professor - on whom she has a secret crush. While Rand gets to know "eighty-year-old Rebecca," Becky is falling deeply in love with him. Can love have a chance when "Rebecca's" truth is revealed? Will Rand believe it was a terrible fraud or a beguiling masquerade?