My DD has also had her share of teachers that have subtly (and some not-so-subtly) made her chronological age or asynchrony an issue even when it had no legitimacy.
Ironically, one of the very worst offenders was a teacher who was very quick to inform us (as parents) that she was herself a gifted student, you know-- so she understood everything about teaching a student like DD. She was pretty derisive about radical acceleration and often looked for ways that DD was "immature" or "not well-prepared" (subjectively so, I must say).
The continuous sniping from some teachers was pretty toxic, and bewildering to me-- nevermind to DD herself.
At the same time, DD usually had the ability to be fairly sanguine about their behavior. It was a pretty strange thing to have my then-10yo sigh deeply and ask me not to "do anything" about "Ms. _____" because "she really just needs to do this in order to make herself feel better about her own abilities and how smart she is."
Bingo. This was Ms. I-was-a-gifted-student-you-know.
My guess, having interacted with her over a period of about 6 years? MG. At most. There was definitely a sense of needing to connect the dots for her, and waiting for her to catch up, when communicating with her over some point of logic that seemed almost intuitively obvious to everyone in my household.
So basically, she wanted to believe that students like DD are "no smarter than" she is/was, and the reality is that someone like DD is as comparable to her as she is to a student who needs a self-contained classroom to accommodate a severe intellectual disability.
It was the fact that my 10yo innately understood that there was no way to intervene to make that situation BETTER-- well, that's DD. This is an aspect of her that has made radically accelerating her rather painless. She understands unwritten social rules and people so well that she can very fluidly adapt to almost anything. Her solution for Ms. __ was to give her PRECISELY the formulaic work-product that she wanted, and nothing more, nothing less, no surprises, no great insights, no subtlety, no deeper analysis.
