Nick stood up. He had never had a towel in his mouth before. 

“Say,” he said. “What the hell?” He was trying to swagger it off.

With these lines, Hemingway gives a nod to Nick’s youth and inexperience. Nick has never faced such a humiliating and perilous situation before. Despite going through such a terrible, near-death experience, Nick’s feelings of uneasiness are hidden beneath a sheen of “swagger” to prove to himself and those around him that he’s not affected by the killers. This detail serves to provide more insight into Nick’s character as someone who would put on a show of bravado rather than admit he feels uncomfortable or afraid. This “swagger” could be seen as a sign of immaturity, as Nick has no idea how to process the situation. Rather than focusing on feeling emotions or acknowledging what happened, as Sam does when he touches the corners of his mouth where the gag was tied, Nick leaps into action, choosing not to dwell on the fact that he was tied up and threatened with death only minutes earlier.

“Mixing up in this ain’t going to get you anywhere,” the cook said. “You stay out of it.” 

“I’ll go see him,” Nick said to George. “Where does he live?” 

The cook turned away. “Little boys always know what they want to do,” he said.

Sam sees Nick’s decision to visit Ole as a marker of youth and stubbornness rather than of courage. Sam indicates that he has experience with dealing with people like Nick, or he has been like Nick in the past but has since learned to act and think differently. 

While Nick’s age is unknown, he’s most likely a teenager or young adult, and Sam referring to him as a “little boy” shows just how much disdain Sam has for Nick’s choice. Sam sees thoughtfulness and the ability to re-think decisions as the traits of an adult. In his mind, Nick is still an immature kid who won’t heed the advice of those around him, even when they’re trying to keep him safe. In Sam’s mind, Nick has not grown at all by the end of the story, instead only revealing his immaturity and naivety.