The commenter said

> I was as much as a year younger

This allows for a range. And as in the example of my own class, not everyone was a year younger than everyone else; that would be impossible. But a large portion of the students were close to or more than a year younger than a good portion of other kids in the class and this showed in academics or athletics. Most of the birthdays in our class, that we celebrated, were Sept/Oct or Feb/Mar, relatively few in the Nov-Jan span, Apr/May and unknown in the summer months. And especially at those younger ages, it doesn't even have to be a full year, even a matter of 2-3 months is a big difference. A child who is 5 years and 3 months will, on average, have an advantage over a child who has just turned 5.