Origins
The English adjective 'old' is one of the language's most basic words, and its etymology reveals a beautifully concrete origin for an abstract concept. It descends from Old English 'eald' (with the variant 'ald'), from Proto-Germanic *aldaz, which is the past participle of the verb *alan, meaning 'to grow' or 'to nourish.' To be old, in the earliest Germanic conception, was simply to have grown — to be a 'grown one.' Age was not measured in years but in the accumulation of growth.
The PIE root behind this is *h₂el-, meaning 'to grow, to nourish,' one of the most productive roots in the Indo-European family. Its descendants span an extraordinary range of meanings across the daughter languages. In Latin, the root produced 'alere' (to feed, to nourish), which gave rise to 'alimentum' (nourishment, source of English 'aliment' and 'alimentary'), 'alumnus' (literally 'a nursling,' one who is nourished), 'alma' (nourishing, as in 'alma mater,' nourishing mother), and most strikingly 'altus' (high or deep, literally 'grown tall'), the ancestor of English 'altitude,' 'alto,' 'exalt,' and 'altar.'
The connection between 'old' and 'altitude' is not immediately obvious but is etymologically direct: both trace to *h₂el- through different suffixation paths. What is old has grown over time; what is high has grown upward. The root's semantic range — encompassing nourishment, growth, height, and age — reflects a worldview in which all these concepts were facets of the same fundamental process.
Proto-Indo-European Roots
Within Germanic, Proto-Germanic *aldaz produced a uniform family of cognates: German 'alt,' Dutch 'oud,' Old Frisian 'ald,' Old Saxon 'ald,' and Gothic 'alþeis.' The Old Norse form was 'aldr' (age, lifetime) rather than an adjective, and modern Scandinavian languages use 'gammal/gammel' (from a different root) as their primary word for 'old,' though the *ald- root survives in compounds and proper names.
The Old English form 'eald' underwent a regular vowel change: the 'ea' diphthong (from earlier 'a' before 'l' plus a consonant, a process called breaking) simplified through Middle English to the modern vowel. The loss of the initial 'e' in standard English (producing 'old' rather than 'eald') was a natural phonological reduction. Dialectal forms like 'auld' (preserved famously in Robert Burns's 'Auld Lang Syne') retain the older diphthong.
English 'elder' and 'eldest' are the original comparative and superlative forms of 'old,' from Old English 'yldra' and 'yldest.' The regular forms 'older' and 'oldest' developed later by analogy, and both sets now coexist with a division of labor: 'elder' and 'eldest' are used primarily for people (especially family members), while 'older' and 'oldest' are used for both people and things.
Old English Period
The word 'alderman' (a civic elder) preserves the old form directly: an alderman was literally an 'elder-man,' a senior member of a governing body. This compound dates to Old English and reflects the ancient association between age and authority that pervades Indo-European cultures.
'Old' has also developed a rich set of figurative and affective uses in English. 'Old friend' implies not just duration but warmth and intimacy. 'The old country' carries nostalgia. 'Good old days' romanticizes the past. 'Old boy' and 'old chap' use 'old' as a term of casual affection in British English, entirely detached from any implication of age. These affective uses — where 'old' means familiar, comfortable, established — are uniquely English among the Germanic languages and have developed primarily since the seventeenth century.
The Old English period also had the noun 'yldu' or 'eldo' (old age), which has not survived into Modern English except in the poetic or archaic 'eld.' This loss left 'old age' (a phrase rather than a single word) as the standard expression, a gap that other Germanic languages fill with single words like German 'Alter.'