"You’re such a silly boy." She kissed me. (16.20)
Frederic gets called a boy a lot. Since we don’t know his age, we don’t know if this is a literal reference to his age. Hemingway was only 18 when he worked as an Italian ambulance driver, but we only get small hints about Frederic’s age, some of them contradictory.
Lying on the floor of the flat-car with the guns beside me under the canvas, I was wet, cold, and very hungry. (32.1)
Frederic perform almost superhuman feats, but when it gets right down to it, he’s willing to admit it that he’s human like everyone else. This comment is a subtle way of reminding us that men have limits too, as the novel shows us in other not so subtle ways.
"I tried not to think and to be perfectly calm." (41.241)
Though things are changing as we see that men and women aren’t all that different, shows of emotion are thought to be feminine behavior, while calmness is thought to be masculine. We wonder if this is just Frederic’s personality, or if he’s learned that calm and collected is the way men are supposed to be.