8 parts Ongoing Katsuki was a late bloomer. He didn't get his quirk until he was seven years old.... At least that that's what everyone else thinks, including his parents.
You see Katsuki got his quirk when he was three and a half, normally a child would have told someone, but Katsuki is anything but normal. He managed to keep it hidden for years, that is untill he was five about to turn six.
When he was five, his birthday just around the corner, Katsuki met All For One. Instead of freaking out about the villain, he was curious, and his curiosity is what leads him down the rabbit hole of villainy.