Swimming on the Moon (1999)

Senior citizen and felon Thomas Hatch is awarded a ninety-nine-year sentence. Hatch avoids the prison term by faking senility and is sent to an elderly facility. There he meets and falls in love with Fiona, an elderly woman who suffers from Alzheimer's Disease. Fiona lives each day of her life waiting to die. Fiona eventually learns about Hatch's falsehood. She promises not to disclose his secret under the condition that he promises to kill her.