I tabled that question and plugged along on the outline. And then --
There's a teenaged boy with powers. Rather isolated. I will mention not getting along with other teens with powers, which is easily plausible given the tiny size of the population, most youngsters not manifesting superpowers.
Then I remembered that the children of the superpowered can live in the same location as the superpowered. The reason he has so few others his age even as possible friends is that those kids are younger than he is. So the beginning is -- twelve, fifteen years ago. The heroine of the story is even able to vaguely remember the first days. Old superheroes are those who gained their powers old, not those with vastly more experience than the young whippersnappers, though there was time for some to be more experienced.
Hmm. While most children of superheroes will develop powers from where they live, it will also not be until their teens or adulthood -- and occasionally late childhood, as for the children who aren't. Going to be some interesting architecture while they work out how to keep that safe. . . .