I think ZUN changed his mind about Reimu's apparent age in the process of making HRtP.
But since ZUN mentions EoSD takes place shortly after MS, it's pretty much busted.
Anyway, I think this debate's pretty much done, seeing as how we're descending into memes.
Maybe Zun just wanted her to stay around 14 - 16. Maybe her Yin-Yang orbs let her do this?
Wouldn't do much for Marisa and everyone else, though.
Environmental maybe?I mean, with all the miasma in the forest and all...