How do Ichijou and the rest of the students have powers?

Question

In Episode 1, it is explained that after the incident 10 years ago, breast-feeding children received supernatural powers which they can use to combat phantoms. Generally, babies are breast-fed for 12 months, so babies with powers should be 11 years old or younger. However, the main characters are in high school, which puts them well over this age specification. How did they get their powers?

Answer 1

Maybe you heard or read wrongly but it clearly says over a decade ago, which places it to be 10-19 years, so the maximum age would be 18 considering a 10 month gestation period for the child and maybe even older if the child was already born during the outbreak.