So far Fenrik looks good, though I would like you to add more detail to his background and appearance. (What does his armour look like beyond the marks of repair?)
Remember that while Neutra is the world in which the Relictors recruit from, there is no regular schedule for when they would come to get aspirants. If there was a tradition of his village, that a certain sign would be a prelude to the return of the sky warriors (Relictors), than that would explain why his village would emphasize the importance of its youth.
Now the reason I want more detail is because you state that he was almost not chosen, but why? Marksmanship would not likely be a key indicator of selection; chapters need youths in peak physical condition after all.
I am also going to deny your chosen nickname for Fenrik. I understand the desire for such a thing, and have no issue with members of each squad to refer to each other by names like that, but a nickname is like a title, it is earned through deed and action to reflect how others view them. So in this case, perhaps Kyron will choose to refer to Fenrik as ranger or hawk-eye or something similar; you never know.
Also, Fenrik can wield two bolt pistols however he will be limited to a chainsword and not the chain-axe.