I see nothing wrong with this. Kid has spare time, he has a hobby, he is very creative and he's definitely spending his time the way he should; doing what makes him happy and what he's good at. Since when does a hobby that involves weapons implies serial killers and people that want death to others? A lot of people are attracted to weapons, a lot of people train professionally, but you probably wouldn't even know that if you saw them. They sure as hell don't look any different. If you saw me on the street, you would have never guessed that I collect weapons. My room is filled with real knives, shurikens, swords, firelocks, spear, axe, and will certainly be filled with more (and I've always wanted to fill my room with those, since I was a kid), but I sure as hell do not have aspirations to kill people. Judging this kid based on his harmless hobby is just as ridiculous as judging anything else, including games and saying they make people violent. Sure, somebody can get hurt if the kid plays around with those, but you can get hurt accidentally by any household appliance.
As for kids today, regardless of this, I can't say much. I've seen awful kids and I've seen good ones. It depends on which ones you see more. And older generations always complain about youth. It was always like that, nothing new about this sentiment. And I'm honestly more worried about kids without ideals and goals than about a kid that has a creative hobby for his spare time.