Casting calls are not accurate character descriptions. They want an actress in her 20’s, but that does not mean the character is that age. Then we have the whole mental age versus biological versus chronological age thing. She could look 25, be over millenia old, and act about 5.
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“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass