Perfect 10 Liners Timeline

The whole crux of Yotha and Faifa being in the same grade/ year is based on Yotha being born at the beginning of the year and Faifa at the end. But Yotha’s birthday is April 8th. I ain’t too good at math, but like 6 weeks is the general time you wait to have some fun. That puts the action in May. And then Faifa would have been born in February the next year if he was full-ish term. They didn’t define if he was early or not… but the timeline doesn’t match. Am I the only crazy one?