The novel is set during World War II. So going away to fight in the war was on all the boys’ minds. There was a draft and a sense of duty. There was much more domestic and international support for America and its allies than more recent wars like Vietnam and Iraq. Before the boys reached the age when they could be drafted, they simply remained at school. There is generally a sense of moving from innocence to maturity during those ages (13-18) but this was underscored by the fact that going to war created an even more pronounced divide between innocence and maturity since war was a harsh reality; and Gene even mentions this.
Since most young men were away fighting in the war, many of the interim teachers were much older. They seemed to recognize that the school was a stark contrast to the war and allowed the boys more freedom than they would usually have. This increased the contrast making the school more youthful than it otherwise would have been. Many of the boys are aware of this but they are also interesting in growing up and accepting the reality of the war. Finny says the war is a joke; this is a denial of reality and a refusal to accept the loss of the sanctuary that is the school and the innocence of their youth. Gene was always more inclined to accept the progression to adulthood and the reality of the war. Gene never really hated Finny; Gene was jealous of Finny’s outlook on life. Gene could not deny the inevitability of growing up and war itself. Finny could. Gene was as jealous of the way Finny could think this way as he (Gene) was of losing his own innocence; of having to grow up).
Finny expresses this spirit of youth more than any other character. He is confident, free-spirited and imaginative but innocent to the point of being naïve – all in an endearing way. The school represents a “separate peace,” a world apart from the war, and Finny is the star of that world.