There are several key differences between us/England etc and other nations who are leagues ahead of us. Starting age is most certainly not the only one. But it is a factor.
They start their kids at 7
No standardised testing like NAPLAN's, rather the teacher constantly assesses in class
They have much shorter days and shorter terms (so more holidays).
They have a different philosophy to learning - it tends to be quite play/inquiry based but still within curriculum perimeters with measurable outcomes. So in between Steiner and what we have now maybe?