It does tend to take the wind out of my sails sometimes lol when you're all 'oh there's no way you can expect us to ever buy that actor as 17', but then on occasion there really are 16 and 17 year olds that look a lot older then you would have thought. I didn't think that Eliza looked all that old, especially in the early season 3 episodes, but I certainly wouldn't have put her at 17 either. A lot of it was in how confidentally she carried herself, whereas Michelle did more have that awkwardness and gawky body language that we generally associate with teens

And heh I did fanwank it to an extent in season 5 because it was understandable that the monks would would to implant memories and instincts to make the people around Dawn be over protective of her, and there seemed to be the occasional wink to it even with Dawn complaining that at 14 she's old enough to be a babysitter, or Buffy not wanting Dawn to go across the street to see her friend because 'I don't like you hanging out with someone that short'. It was mostly season 6 where it started really bugging me with Tara still asking Dawn if she wants her pancakes made in funny shapes when Dawn was pushing 16 that season ffs, although I suppose it can be argued that the protective urges towards Dawn just naturally carried over from how they remembered always treating her