It depends on what your conception of elvish immortality is. For instance, you could postulate that the defining feature of elves is that they do not change, m

It depends on what your conception of elvish immortality is. For instance, you could postulate that the defining feature of elves is that they do not change, mentally as well as physically, once they reach maturity. Their personality crystallizes, as firmly as their biology, and whatever happens to them over the millennia they live, they will remain themselves. This makes them very different than you and I, but IMO it's also very compatible with the way elves are presented in Tolkien.