Not necessarily. Maturity in teens isn’t about age really. You get some 8th graders looking like high school seniors, and get high school seniors looking like 8th graders.
Kids that run fast times in high school for the most part reach puberty faster, it’s rare looking through past NXN champs that you see an extremely short and scrawny kid. They’re all developed, which means they need to start adding on the training more.
Chances are that Erriyon keeps training with his same coach for a couple years before switching to a pro coach. There’s no reason for a high schooler to be racing against kids who he is much faster than. If you don’t have competition in practice and in racing then you are going to lose the drive that makes you want to get faster.
Like another guy said, sprinting is a young mans sport. I’m not saying he should go balls to the wall at 16, but he needs a faster environment for the long term