Most superheroes are teens actually. It's a trope of the medium and genre.
What ethnicity, age and gender should a writer create? Should all new characters be white males? What if I wrote a comic where a kid transfers Hulk's powers to himself; who decides what the age, ethnicity and gender of that character?
It is entirely possible Riri Williams is just a new character. Who happens to be female and black created by a white male writer.
As I mentioned above in reply; who decides the gender, ethnicity and age of new characters if not the writer? Do writers have to obey rules created by... ?
Hm. So then you are unfamiliar with the nature of continuity based superhero comics? This is pretty common stuff.Whatever, I don't read comic books anyway.