i'm going to have that same experience, as my 2nd daughter was born on nov. 5 and she misses the cutoff date. in my town it is oct 1. so, she just started preschool and she will go again next year. she is going to be 4 this november, so when she starts kg, she will be going on 6! i had the opposite problem with daughter # 1, whose bday is aug. 27. she is one of the youngest in the class, and her preschool teachers had recommended 'redshirting' her (that's what it's called when you voluntarily hold your child back for an extra year) i think you'll find a lot of parents of boys choose this option because boys tend to mature a bit slower than the girls. we chose to start her in kg, and it worked out well for us and for her. but, really, i am not worried about my little one. it gives her an extra year home and in preschool, and although my career track is on hold until she starts her formal education (costs too much for daycare!) i have committed myself to enjoying these next 2 years as my baby grows into a little girl.
i do believe that private schools do not follow the same rules as public schools when it comes to age. there are no special tests that you can take to start public school at an earlier date. the cutoff date goes by age, not ability.