If the mane six or seven are seniors, what the hell is Big Mac doing at their school? He's older than them, isn't he??? Unless he visits the school a lot as alumni, I don't get it one bit.
Maybe Fluttershy has a weird birthday like I do. She would have started Kindergarten at 4 but she got held back from starting until she was 5. That almost happened to me but it didn't. Fluttershy started senior year at 17 and graduates at 18. I started at 16 and graduated at 17. Go September birthdays