I made a mistake back when my daughter was that age so I'd like to share it with you. She was making A's in preschool and she was very slightly taller than the other kids. Also, it was like free daycare which would help the financial burden.
So, I thought I'd put her in early. Her b-day was 9/5 and I had the choice back then because she'd been in private preschool and kindergarten. The school begged me not to put her in early as it tends to be harder on kids in general. I thought "my child" was the exception.
In third grade, she cried a lot in school over little things and had trouble with reading comprehension (which is when, I'm told, when any learning differences start showing up). Over the years, I finally got a diagnosis of A.D.D. with an associated learning difference and chemical depression and a sleeping disorder! Oh, and she didn't grow to be tall. She never got past 5/3".
What we went through over those years to learn and overcome was horrible. Good part was that with all the help from me and counselors, she graduated college. She is very talented, smart in many ways, and the A.D.D. meds helped her easily understand what she read and remember it better.
I now can't think of one good reason to push a kid in early. I now realize that allowing them more time to mature, learn more about the world and socializing with kids and adults, following rules, etc. would have been better. Provide them another year with increasingly more and more responsibilities, expectations, and various children.
Having to sit in a school chair for much of the day with far less activities and fun learning experiences can be a challenge in itself for little ones. And homework nowdays is far heavier than it used to be. You may find yourself frustrated with the time you have to spend helping them stay focused on it and get through it all. (I do wish they'd modernize our old style teaching methods to be more like the Montessori type.)