The Quirk appears at age four.
Not five, when school begins — not seven, when cognition stabilizes, but four, the moment a child can speak but cannot yet lie convincingly to themselves about who they are.
The visual grammar does the work. Early episodes show quirkless children watching their classmates develop superpowers with the flat affect of a medical diagnosis being read aloud.
But the real revelation is what the show does with Deku's quirklessness — it treats it not as tragedy but as administrative error. His trajectory becomes about fighting the system's verdict, not discovering an authentic self. He wants All Might's power, he wants to be ranked, he wants to pass the entrance exam — but he never asks what he actually wants to become, and the show never lets him.
The real horror isn't that Deku has no power — it's that every character with power still can't choose what to do with it.
Rewatch Deku's quirklessness reveal (Season 1, Episode 1, around the 8-minute mark) and notice what's absent: not magical hope, but any conversation about what he wants to be versus what the system says he can be.
Find Takeshi Yoro's 'The Brain and the Void: On the Phenomenology of the Body' (Japanese philosophy on biological determinism and social foreclosure)—it reframes how the Quirk system functions as visual metaphor for Japan's postwar educational anxieties about fixed identity.