I am not sure what to think. I mean, seeing Spike be so "Real" for a few moments, he shows concern for Twilight, but isn't sure what to do. That shows his immaturity and naivety. It is a real moment of fear for him and maybe for some readers. We laugh at this joke, but think of it from Spike's view. He will always remember in him a bit of Twilight as she acted in this comic.
Also, to be fair again, girls can get yeast infections down there without having done anything crazy. But yeah... Prob teen range.