Fyi: it’s called post secondary because, I think, UK calls it primary, secondary, and after that is post secondary.
For my state in Australia its
Kinder Ages 3-5
Prep Ages 5-6
Primary School Ages 6-12, called Grade 1-6
Secondary/High School Ages 12-18, Called Years 7-12
After that you’ve got higher education choices via TAFE or University, theres no cut off ages for that.
School is mandatory from ages 6 To 17.