Most schools will allow a 4 year old to enter kindergarten if they turn 5 shortly after the school year begins.  Take a look at the response here to get a better idea:

if you are low income then you can put your child into a headstart program. if you are not low income chances are that you're child may not be applicable. should that be the case then you can probably put your child into preschool at a daycare located near by you at price. and depending on when your child turns five you may be able to get them into kindergarten (the cut off date is ussually august 31st so if your child doesn't turn five before then, more than likely they will not be accepted into kindergarten).

WHY would you want him to?
 
I can address this on a couple different levels, but mainly as a parent who started their son TOO early!
 
We started our youngest son in school as early as we could. We recognized very early that he was extremely bright! So we listened to all those voices telling us we needed to start him in school ASAP!
 
The good news - He NEVER struggled with any of the curriculum at any level...in fact, he was usually light years ahead of nearly all of the students in his class.
 
The bad news - He was always the youngest in his class...which seems like no big deal...until down the road. Everyone else was driving...he was not old enough to take driver's ed. AND... Since boys mature later than girls, he was constantly doing goofy stuff (to get a laugh)...stuff that was age appropriate, just not grade appropriate...so we pretty much wore a path to the principal's office in every school he attended. Since he was so bright, when we would ask what he was not getting done...the teachers & principals would just say he wasn't having a problem with any of the curriculum. In fact, in most cases, he was helping students in the class that were struggling.
 
I just know that if we had it to do over again, we would have kept him home until he was older...I think it would have saved him (and us) lots of grief! Also...we can't go back in time and spend those early years that we sent him to school together...once you send them it's a done deal!
 
I know that as a parent we all want the best for our children, for them to have an edge or advantage in the world we live in...but what could be a greater advantage than for children to have extra time at home with their parents...to have even one extra day with those who love us the most seems like such an amazing thing...let alone a year...or even two!
 
Think it all the way through...down the road looks a long far far away...but it will arrive WAY sooner than you think!
 
I hope this helps...