Well I don't know what redshirt is, but both my boys started preschool in a 3yo class when they were 2. They both have fall birthday. They both started kindergarten at 4.
My oldest who turned 18 Sept 30th, is a freshman at an engineering school this year, on merit scholarships.
Next son is a junior in high school, will be graduating next year with an Advanced Regents Diploma.
If they were 'socially behind' when they started K, than they're STILL socially behind, it's made no difference to either one of them to be the youngest in their classes. They have not been unusually challenged by school, and furthermore may have been quite bored if I HAD waited a year.
That said, now in hindsight, I wonder, what's the big rush? Now that one is gone and the other gone next year, I almost wish I'd waited too, like seems to be the popular thing to do. Least I'd've had them home for one more year, sigh.
You do what feels right in your heart as their Mom. If YOU say it's right, than, of COURSE it's right. That strategy seems to have worked for me in all things motherhood.
Enjoy him!
:)