For many years one's date of birth determined whether the child began kindergarten in September or in February. If the child was five years old before November 1st (correct me if I'm wrong on the date) he/she began school in September of that year. If not 5 before November 1st, then the child's starting date would be February.
It was thought that children would not be mature enough to cope successfully if starting Kindergarten too young.
I was one of those who started in February. The next September came and I spent three days in 'high' Kindergarten when, due to my superior intelligence, (or maybe I was a brat) I was promoted to first grade! So I ended up being a June graduate.