You have two kids. The oldest is 5 years old. His birthday is in November. The youngest is four, his birthday is in October. The cut off for starting school in your state is October 16, which is right after the youngest has his birthday, and right before the oldest has his.
So the older will be 5 turning 6 when he goes to Kindergarten, the younger, will be 4 turning 5, assuming you start him the same year.
What do you do? Do you start the younger kid this year and have both kids in the same grade together, or do you hold him back a year?