I noticed something about Milky, the MA Survival PV showed her to be reletively the same age as Elluka and showed her as an adult with Pale; however, when Pale was still Pale and with Milky, Elluka was still a child. While we'll need the second novel to be sure, there is a chance that Milky and Pale's relationship was retconned into being pedophilia. Meta also reffered to Milky as a "brat" with Price stating that her age was unknown, but likely young.
Of course this is partially just speculation. Since Milky was a good enough mage to be a MA candidate, she could possibly be using magic to look younger, or something.