seventy-five-year-old

the term is a modern english compound, directly constructed from its constituent number and descriptive phrase. "seventy" derives from old english "hundseofontig", meaning "seven tens", via a common germanic pattern. "five" originates from proto-germanic "fimf", from pie "pénkʷe". "year" comes from old english "ġēar", from proto-germanic "jērą", likely from pie "yóh₁r̥". "old" stems from old english "eald", from proto-germanic "aldaz", meaning "grown up". the hyphenated construction "year-old" as a unit for stating age became standardized in modern english, with the numeral prefixed to create specific age descriptors. the logic is purely syntactic, combining a quantifier with a standardized age unit without metaphorical or semantic shift from ancient roots.

this is a compound adjective/noun formed from the numeral "seventy-five" and the hyphenated adjective "year-old". it is not segmentable into classical morphemes as it is a modern english syntactic construction.