Attendance at school, despite what many people think, is not compulsory: Parents of a child of compulsory school age are required to cause him/her to receive efficient full-time education suitable—
a: to his age, ability and aptitude, and
b: to any special educational needs he may have,
either by regular attendance at school or otherwise.
So as far as I am concerned you can have your children start school when you think they are ready.
Of course, this may give you a battle as organisations don't like their neat rules being messed about with. Nor does everyone have the luxury of staying at home with their children. I kept my eldest at home until he was six. We did some "work" everyday but mainly followed his interests. When he went to school it was a full year before he was asked to do anything he hadn't already done at home.