J.K.
I have a 4 year old son with a birthday just after the cut off date and I work in a public school and the best advice that was given to me was to not push putting him in school. There is a reason for the cut off dates and boys especially need that maturity and focus to start out school on the right foot. My son was not ready to start school when he was just turning 3 and now at 4 (almost 5) he will be starting preschool. Next year your son will be elegible to start Shining Stars Preschool and it is an excellent preschool that is free (if you live in Rio Rancho city limits) because it is run by the district. The application deadline is in April for 2009-2010.
If your son is extremely gifted and you believe he is ready for school, he can be tested and the school can then review those tests and admit your son. There are ways around it, but I wouldn't push it unless you strongly feel your son is ready.