The original comparative of 'old' — Old English 'ieldra,' literally 'more grown,' from PIE *h2el- (to grow).
A person who is older, especially one who is respected for wisdom and experience; also the comparative form of 'old' when used of family members.
From Old English ieldra (older, more aged), the comparative form of eald (old), from Proto-Germanic *aldizô (older, comparative of *aldaz), from PIE *h₂el- (to grow, to nourish). The word originally functioned purely as a comparative adjective meaning 'older' but was substantivized early in the Germanic languages, developing the noun sense of 'an older person, a person of authority by virtue of age.' This semantic shift from comparative adjective to social title reflects the deep Indo-European association between
English has two comparative forms of 'old' with different functions: 'older' is the regular comparative used for any comparison ('this building is older'), while 'elder' survives only for family seniority ('my elder brother') and for the noun sense of a respected senior person. German keeps the same split: 'älter' (older) vs. 'Eltern' (parents, literally 'the older ones'), showing this distinction is ancient.