from what i've gathered as to the nature of aman, immortality is not a property of the landmass itself, but rather its sapient inhabitants; the prohibition against mortals is not about the acquisition of an indefinite lifespan by humans who set foot there, as it is about making a sacred (not holy) space for those with indefinite lifespans. in addition, the landmass of aman is supposed to be free of this so-called "Melkor element" that suffuses middle-earth down to the quantum level.
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the Staff of the Halatir of the West
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