This was excellently written, as expected from a story that got so much editorial attention and critical acclaim. But, like others, I was left with mixed feelings about the tropes and the foreshadowing in the execution of them. My favorite story with this kind of adolescent plus older partner in crime setup was Gemma Files' Emperor's Old Bones story, though that one was grimly cynical from the start, whereas this one attempts to creep up on you. Files' story also reversed the genders and ran with the possible romantic connection as a plot point. Naturally, both stories end up in the same place though - the dinner table.
What I like to think is that while, yes, the story is a bit on the nose with its foreshadowing and literary references and so on (I think the average horror reader can guess well ahead of schedule where talk of eating life force and such is headed in a story.), it is still an enjoyable attempt by the author to play with some pretty familiar tropes involving a very young character with an older mentor, with the issues of attraction, and potential sexual tension, often seen in such stories thrown into the mix, but in a way that could subvert our expectations.
The author must have been aware of this possible expectation on the part of the reader regarding a vulnerable young character, and the story accordingly swerves around this issue while never completely leaving it. The younger character muses on occasion on the older one's appearance, age and possible attractiveness, even though she at first insists she can't imagine his being appealing amidst all this sizing up. We eventually discover that her view of him as ancient is more tied to her own perspective as a very young person as he is not really a stereotypical elderly sorcerer, but only in his thirties throughout the story, even as she seems to relentlessly grow closer to him and passes judgments on his associating with any others besides herself romantically. But then, any even potential advances are only made by the teen, and are firmly rebuffed by the seemingly caring older person as the reader is gradually invited to view his caring as sincere and the relationship boundaries as appropriate, and perhaps even a healthy alternative to the company of her alcoholic father. And so, a tender story of growing up with help from a caring special someone is revealed? Um, no.
Of course, then the hammer we all knew was coming finally falls, and the mentor character even straight up states that he has in fact taken advantage, just not in a sexual way, by having knowingly eaten her childhood, and has brought her to something perhaps worse than victim-hood - having groomed her instead for becoming a killer. All along, the encouragement of reading, learning and growing maturity was all just a setup for eventually having to deal with the reality of the feeding.
The reader also must come to the conclusion that the premature aging of the mentor will be passed onto the apprentice. This seems a particularly raw deal, considering that cannibal or vampiric pursuits usually impart youth in these kinds of stories. Not so here, as it's all a big pit of ravenous consumption, of others, of the self, of childhood, and even of one's very vitality. For what? Being able to move marbles around with your mind? Maybe something more, but we never find out what that may be. But then, those learning a craft often do work themselves to early aging through obsession, and misery loves company. So I suppose it all makes a twisted sense in the end.