The inner life of Benjamin Button, abandoned at birth by his stricken father (Jason Flemyng) and raised by the infinitely kind caretaker of a nursing home (Taraji P. Henson), is harder to grasp than his outer appearance, in part because Mr. Pitt seems more interested in the nuances of reticence than in the dynamics of expression. It’s true that Benjamin’s condition imposes a certain detachment: he is at once innocent and ancient, almost never who he appears to be.