Richard Linklater has long had an interest in the travails of young suburban men lurching through life's changes. From "Slacker" to "Dazed and Confused," "Boyhood" to "Everybody Wants Some," he has been their chronicler, if not their cheerleader. With "Last Flag Flying," the 57-year-old director and Houston native trades "Boyhood" for manhood, painting a well-observed portrait of middle-aged Vietnam vets in the throes of an emotional crisis sparked by the death of one of their sons in the Iraq War.