This kid has been showing up in news feeds, but only credulous pop media articles, not hard science reporting. What did he build, and what physics does his device do?
He built a fusor. It's basically a small particle accelerator designed to fuse atoms together. It can be used as a neutron source or to produce commercially useful radioisotopes. It doesn't produce any net power- the acceleration takes far more energy than the fusion produces even if all of that energy could be harnessed, so calling it a "nuclear reactor" is more than a little misleading.
You don't see it in hard science reporting because it's not notable from a scientific standpoint: anyone with 10 thousand dollars, some technical skills, and sufficient free time can build one in their garage.
$\begingroup$ Well, it is a device which produces nuclear reactions, it's just endothermic overall. In the same way that the phrase "chemical reactor" denotes a device used to produce chemical reactions, regardless of whether they're exothermic or endothermic (with most real-world cases being endothermic). $\endgroup$ Feb 23, 2019 at 12:59
2$\begingroup$ It's also a sad testament to the ignorance and lack of effort of many journalists whose lot in life seems to be to repeat what someone else reported without digging deeper. Plenty of teenagers have made fusors, although it may be true that he's the youngest, but how can that be verified? BTW, I've seen his age reported variously as 12 and 14. Can't they check the simplest facts? $\endgroup$– garypFeb 23, 2019 at 13:04
3$\begingroup$ @EmilioPisanty I don't disagree that it may be technically correct (the best kind of correct), but to a layperson "nuclear reactor" means a device that produces power. A headline of "Boy Creates Nuclear Reactor" without any clarification is misleading at best. $\endgroup$ Feb 23, 2019 at 13:54