It seems you are in a particularly good spot to make this call, given you are a K teacher. Six weeks is not long after the cutoff at all. I wouldn't make the decision based on college entry age. There are 13 years between K and that time! Much can change in society and in her options. Gap years may even be the norm by then...
I do have some personal bias, having started at 4 with a Nov. birthday. Starting college at 17 was absolutely fine. I turned 18 a few months later. Waiting a little longer than most of my friends to drive at 16 was sort of irritating, but frankly, I'm not sure 16 year olds are fully ready to drive!
