Two and one-half stars. Rated R. 93 minutes. With his shock of white hair, crosshatched tan skin and deep, sonorous voice, 72-year-old Sam Elliott seems less human than something forged out of silver, leather and smoke. He’s long been a valuable supporting player, whether on-screen (“Grandma,” “I’ll See You In My Dreams”) or mostly off (“The Big Lebowski”). In “The Hero,” Elliott finally gets to claim center stage, in a role that often slyly invokes his iconic stature and voice.