I realize this is too late for OP, but may help someone else.
I'm that guy, I have a late November birthday and was put in the class ahead of where I was supposed to be.
Pretty simple way to do it, private kindergarten and first grade, public school didn't really have much choice when looking at the marks from first grade as they were pretty good. It worked in the early 80s, no idea if it'll still work.
As far as being the youngest, it was never an issue, I accepted it and moved on. It forced me to grow up quicker competing against kids who were as much as 14 months older than me. Call it an early dose of tough love.
Overall, I think it was the right move, had I been with the correct class it would have been much easier in terms of scholastic work as well as school athletic teams.
It is a choice, and in all reality, should be based on what a kid can do and their overall scholastic, emotional, and physical maturity.