Didn't have the same issue with my DS because he's a January baby...but I would just caution you about some outside factors when making this decision. If you care...you may not, that's fine, but I just bring this up for consideration...
You live in a state with a LATE cut off date IMO. In Texas, we work with August or September as the cut off. Maybe you are good to go with your state and not thinking of moving anytime soon, but if you did move, your child would easily be over one year younger than others in their grade. I'm not going to say everyone does, but in my experience, most boys that are born from late May to the cutoff date are held back. Reasons vary, maturity, size, hopeful sizing for sports in highschool/college, etc., whatever, doesn't matter, just saying what I experience as the norm. My January baby that I thought would be smack in the middle of his class is one of the later birthdays in it and he's one of the younger ones in there.
What is the norm in your state? Not that you have to follow the pack, but for the sake of relationships with peers, it sure helps to be along the same development level as your peers...think P.E., think driving, think dating, think age going off to college.
Personally, I think that kindergarten readiness can also be measured with emotional maturity. My DS wouldn't have been ready at 4 to start kindergarten. School is way different than it used to be. He had homework in Kindergarten! Let the stress begin! If you can, I would definitely do one of the tours or open houses that the schools around here do (if you have that) and check out what a day in the life of your school is like. I know that my DS couldn't have eaten his lunch fast enough at that age to get through the school day.
There's a lot more to consider in readiness than sheer "what do they need to know" readiness. I wish you well in making your decision. It's so hard to know the right thing to do for our kids sometimes! I know you just want to do the best by him.
