@Med1um: Her first meeting with White has her being this tiny size too:
https://mangadex.org/chapter/705580/21
And page 6 of this extra has Melissa mentions she's grown up in the dining hall + working with the dragons, meaning she has been dealing with dragons since long before.
So I think the apprentice part is just her earning the job of maid/attendant apprentice, and the extra of book reading happened way before then.
From chapter 1, her coming of age is 16 and she mentions leaving to become actual attendant to a noble i.e. done with her apprenticeship.
https://mangadex.org/chapter/705580/27
And Commander has been coming to the 4th dining hall (i.e. her home) for 10 years:
https://mangadex.org/chapter/741785/16
So the earliest he could've met her was when she was 6.
Btw, she is really strong:
https://mangadex.org/chapter/705580/23
Pushing a cart full of food alone...