Below, you'll see any text that was highlighted with comments from the reviewer.
I think you started with a very strong intriguing opening, which is what pulled me into it begin with, but I felt that the large chunk of background information that immediately followed took away from some of the pull.
I think with a little more focus on specifically the emotions that the main character felt of awe and pride and sorrow could really help hone the set-up and make it more streamlined.
From the get-go, you have a very clear description of the character from the simple act of smoking a cigarette, which
I'm guessing that the narrator is some kind of journalist interviewing the main character about his time, but I'm still a little fuzzy on that; maybe add a few more details about how they've come to meet, and why the narrator is so interested in this topic in the first place.
I feel that the scene of gas attack could be elaborated upon a little more to juxtapose the horror with which he is witnessing with the dull emptiness that he has from witnessing it.
From the main character's very despondent emotional response, we can surmise that the war environment is very taxing; however, I feel as if that a few more details about the harsh conditions of I'm guessing the trenches could add to the despair that the main character must be feeling.
I also feel a little more of the setting beyond just 'cafe' could be useful in setting the circumstances in which the interview occurred.
For starters, your choice of topic of World War 1; it's a very mature subject to talk about compared to the usual fare of fantasy and romance amongst teen writers, and I think that you've managed to address the topic both sensitively, but accurately, which is impressive.
Secondly, your description at the opening was absolutely wonderful in establishing character, and I feel seriously demonstrates your proficiency as a writer. Just keep doing more of THAT.
One thing that works well about this piece is that it is effective as is as a story, with a satisfying beginning and ending, which is impressive within such a short span.
However, I am concerned that the extract doesn't really reference any other part of the story, making it kind of difficult to extend this into a story. I would suggest adding more hints or clues referencing the before and after of this meeting as to where the novel would go next.
And of course, good luck with your entry! Polish it up a bit and I'm sure it'll be very competitive.