Elder Days
The Elder Days, also called the Eldest Days, was a term that, during the Second and Third Ages, properly referred to the times that preceded the Downfall of Angband at the very end of the First Age, perhaps covering not only the entire Age, but also the events before the Awakening of the Elves, by which its beginning was marked. In that context, the Middle Days were the Second and Third Ages, whereas the Younger Days were the foreseen Dominion of Men.
However, in the Fourth Age the term began to be applied to all previous Ages, as the time before the Dominion of Men and the dwindling of the Elves and other races. Aragorn for instance, referred to himself as the last King of the Elder Days, according to the latter sense. In this context, the Elder Days were also called the Elvish World.

Etymology
Tolkien notes that the word "Elder" has deliberately an archaic flavour, since it is now only applied to persons (Elders = seniors). He also pointed to an association with the poetic word eld 'old age, antiquity'.
Early English had the expression Þe eldern dawes 'the days of our forefathers, long ago,' i.e. Days of the Seniors, which was intended by Tolkien.
The "very archaic" Old English name for the First Age that "came" to Arundel Lowdham was frumaeldi.
Referencias
1. Esta ficha se ha importado inicialmente de TolkienGateway.net el día 25/05/2026.