Hello, Australia!
The ages I listed below are the "expected" levels--as we all know, kids move at all different rates, and after we assess, we start teaching where they begin instruction. Does that make sense? Again, just usual ages.
Kindergarten is ages 5-6
Pre-Primer can start in late Kinder and the first half of first grade (6-early 7)
Primer and 1st are usually for 6-7 years old
2nd grade, 7-8
3rd grade, 8-9
4th grade, 9-10
5th grade 10-11