My mum is a kinder teacher (has been for about 40 years now ) who is also qualified for primary teaching. She always recommends that kids start school when they are a little older, in preference to starting early. Again, she cites the high school thing. With my DD she missed the cut-off to start school by one week. I could have pushed the point (as she was "ready") but I decided not to start her until the following year.
If you like, I can ask her opinion on whether your DS would be better to do two years of three-year-kinder or four-year-kinder....