The Great Debate

We are really struggling with the decision on whether or not to send Aidan to Kindergarten in the Fall. He is in a Pre-K class now and his teacher is a retired kindergarten teacher with 25+ years experience. We had a conference with her in October. The funny thing was that I totally prepared Jim that she would say he wasn't ready. To tell you the truth, up until that conference, I didn't really know what he knew. He has never wanted to sit down and "learn" with me. He's so different from Avery. Avery loved doing flash cards when he was little. He loved everything about learning his letters, shapes, numbers, etc. He even enjoyed making a game out of learning his personal information- address, phone number, etc. Aidan wouldn't do flash cards with me if his life depended on it. I'm hard pressed to get him to recite the alphabet. So when I tell you I didn't know what he knew prior to speaking with his teacher, Mrs Harris, I had no idea.
So I walked in to the conference in October fully expecting that he would NOT be attending kindergarten in the Fall. I had convinced Jim of that as well. Imagine our surprise when Mrs. Harris went on and on about what he knew, how well he does socially, and that he was absolutely ready for school. Then... she looked at his birthdate and said, "Except that he's a boy and has a summer birthday."
I've received a lot of information about why you shouldn't send a boy with a summer birthday to Kindergarten when he turns five. It gives him an extra year to mature and it will make him one of the oldest in his class. Let's face it, for boys size matters and the extra year could mean a huge difference in physical stature, especially in high school years.
We go back Monday afternoon for our final conference with Mrs. Harris before Kindergarten registration. I'm interested to see what she has to say now. She was Avery's Pre- K teacher as well and as stated previously, has a wealth of experience as a retired kindergarten teacher.
Here's my question, "Should there be this blanket statement applied to all boys?" Can there never be any outliers?
There are so many things we've looked at- scenarios we've played out in our heads of what will happen if we send him and what will occur if we don't. I have to tell you that socially, Aidan is much more ready than Avery ever was at five. I think that is just a difference in personalities. I'd love to hear opinions. And if you can answer what you would do, I'd love to hear that too.
What would you do if your son had a summer birthday and was by all accounts "ready" in all aspects for school other than the fact that his birthday falls in the summer?