An Etymological Dictionary of the German Language/Annotated/jung
The adjective jung, ‘young, new, recent,’ is the common Teutonic junga- (with a nasal); compare Middle High German junc(g), Old High German and Old Saxon jung, Dutch jong, Anglo-Saxon geong, English young, Gothic juggs (jungs), ‘young.’ This common Teutonic junga- is based, by contraction from juwunga-, upon a pre-Teutonic yuwenko-, ‘young,’ with which Latin juvencus, ‘youth,’ and Sanscrit yuvaçás, young,’ are identical. The earlier Aryan form yuwên (yéwen?) appears in Latin juvenis, ‘young, youth,’ and juven-ta, ‘youth’ (equivalent to Gothic junda, feminine), as well as in Sanscrit júvan, ‘young, youth’ (yôšâ, feminine, ‘maid’), and Old Slovenian junŭ, Lithuanian jáunas, ‘young’; they are all based upon an Aryan root yū̆, ‘to be young’ (compare Sanscrit yávišṭha, ‘the youngest’).