In The Red Badge of Courage, at the end of the battle in Chapter 20, the narrator concludes that the soldiers "were men."
At the end of the battle in Chapter 20, the narrator concludes that the soldiers "were men." He concludes the same for Henry in the last chapter. However, his description of Henry as "the youth" never changes. Why do you think this is?
This is an excellent question to consider. I would want to answer it in two ways.
Firstly, it is important to remember that the action in the novel only occurs over the span of a few weeks. It is easy to forget this, because during these few weeks, Henry in particular undergoes massive changes in his own character, and greatly matures. You are right to indicate that one of the principal ways in which he matures is through the journey from youth to manhood. However, at the same time, perhaps one of the reasons that Crane still uses "youth" to refer to Henry, even in the last chapter, is to remind us that although he is now very experienced and mature, he is still a young man as regards his age, thus highlighting the way in which war makes us wise beyond our years.
Secondly, a key theme of this story is the precise nature of manhood. Throughout the novel we see that Henry changes his idea of what manhood actually consists of. As the novel begins we see that his conception of manhood is based on rather naive and romantic notions as he believes that the more experience he gains the greater adoration he will receive. However, at the end of the novel, Henry realises that manhood is about how we integrate the different episodes of our lives, both the good and the bad ones, without ignoring our mistakes and failures. He is shown to have just managed to start this process at the end of the novel, so perhaps the continued use of the title "youth" indicates that he still has some way to go to reach manhood, which arguably is not an end destination, but a way of travelling.