Ngl, I quite like how the story is going. The fact that they accepter the kid not because he had strength (0 stats on everything), but because he pretty much sacrificed himself to kill the hydra is nice. They also teach the boy in a way that the majority of teachers do not do, I mean, guy literally grew under them because they taught him in a better way than the school did. And considering the species they are (I have my concerns I will admit, especially the elf), the kid should be at the least 20 by the time he's good, or maybe even longer, considering they are S-class and the boy's probably an F (I am praying for time skips to happen).