Origins
The English adjective 'young' traces a clear path from Old English 'geong' (also 'giung') through Proto-Germanic *jungaz to the Proto-Indo-European form *h₂yuh₁en-, meaning 'young' or 'youthful.' The PIE form is itself derived from the root *h₂yew-, which carried the sense of 'vital force' or 'youthful vigor,' connecting the concept of youth not merely to age but to the energy and vitality that characterize early life.
The PIE root *h₂yew- was extraordinarily productive. In Latin, it gave rise to 'iuvenis' (a young person), the direct ancestor of English 'juvenile,' and 'iunior' (younger, comparative form), the source of English 'junior' and 'juniority.' The Latin goddess Iuno (Juno) may also be connected, as a deity of vitality and youthful energy, though this etymology is debated. In Sanskrit, the root produced 'yuvan' (young man), and the Avestan cognate 'yavan' appears in the Zoroastrian texts. Lithuanian 'jáunas' and Latvian 'jauns' continue the same root in the Baltic branch.
The Germanic development from *jungaz is regular across the family: German 'jung,' Dutch 'jong,' Swedish, Danish, and Norwegian 'ung,' Icelandic 'ungur,' and Gothic 'juggs' all descend from the same Proto-Germanic ancestor. The Old English form 'geong' shows the characteristically English palatalization of initial *j to the affricate /dʒ/ (spelled 'g' or 'ge' in Old English), a sound change that also affected 'year' (Old English 'gēar' from *jērą) and 'yell' (Old English 'giellan').
Old English Period
The phonological journey from Old English 'geong' /jeoŋɡ/ to Modern English 'young' /jʌŋ/ involved several steps. The Old English diphthong 'eo' was simplified in Middle English to a short vowel, and the spelling shifted from 'ge-' to 'y-' as scribes adopted the letter 'y' for the /j/ sound that Old English had written with 'g.' The resulting Middle English forms 'yong' and 'yung' directly prefigure the modern pronunciation.
The noun 'youth' is a close relative, from Old English 'geoguþ,' formed from the same root with an abstract suffix. This suffix (*-iþō in Proto-Germanic) is the same one that produced 'truth' from 'true,' 'health' from 'whole/hale,' and 'growth' from 'grow.' 'Youth' thus means literally 'the state of being young,' just as 'truth' means 'the state of being true.'
English 'young' has had a relatively stable semantic history compared to many adjectives. It has always meant 'not old, in the early stage of life,' and this core meaning has not shifted. What has changed is its range of figurative applications. In Modern English, 'young' can describe ideas ('a young science'), institutions ('a young company'), wines ('a young Beaujolais'), and even the night ('the night is young'). These metaphorical extensions, mostly dating from the seventeenth century onward, project the qualities of biological youth — freshness, immaturity, potential — onto non-living things.
Later History
The comparative and superlative forms of 'young' — 'younger' and 'youngest' — are regular, unlike the suppletive forms of 'good' (better, best) and 'bad' (worse, worst). However, the derived noun 'younger' has taken on a specialized meaning in some dialects and historical contexts: 'younker' or 'younger' once meant a young nobleman or knight, borrowed partly from Dutch 'jonker' (young lord), which is also the source of the name 'Yankee' (though this etymology is disputed).
The surname Young is one of the most common in English-speaking countries, originally a nickname distinguishing a younger person from an older one with the same name — 'John the Young' becoming 'John Young.' The German equivalent is 'Jung,' most famously borne by the psychiatrist Carl Jung, whose surname literally means 'young.'