About elves and immortality

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Iv'e just finished reading the Arwen &amp; Aragorn story in the Appendix and i have some questions.

Im not sure about that, but as i understand, the elves get to be immortal only if they , at some point, leave ME and sail to Valinor.

In that case, why didnt Arwen sail to Valinor AFTER Aragorn's death?
She said that there are no more ships that can take her, does that mean all the elves on ME were gone by that time?

and another question, at what point in their lives the elves sail to Valinor? how they decide when is the time to go?

Thanks for your answers


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