The Jargon File (version 4.4.7, 29 Dec 2003):

elder days
 n.

    The heroic age of hackerdom (roughly, pre-1980); the era of the PDP-10, 
    TECO, ITS, and the ARPANET. This term has been rather consciously
    adopted from J. R. R. Tolkien's fantasy epic The Lord of the Rings. Compare
    Iron Age; see also elvish and Great Worm.


The Free On-line Dictionary of Computing (30 December 2018):

elder days

   The heroic age of hackerdom (roughly, pre-1980); the era of
   the PDP-10, TECO, ITS and the ARPANET.  This term has
   been rather consciously adopted from J. R. R. Tolkien's
   fantasy epic "The Lord of the Rings".

   Compare Iron Age.  See also elvish and Great Worm.

   [Jargon File]