The compound 'year-old' is a transparent and productive formation in English, directly combining two native Germanic roots. 'Year', from Old English 'gear', originally denoted a measure of time based on the cycle of seasons. 'Old', from Old English 'eald', carries the fundamental sense of having existed for a long time. The hyphenated compound logically fuses these concepts to create a precise adjectival or nominal descriptor indicating the exact duration of existence, primarily for young children or objects. Its construction follows a common English pattern where a unit of time is appended with '-old' to specify age, making its meaning immediately accessible.

Structure: year (time unit) + old (aged) - year: From Old English 'gear', meaning a cycle of seasons, a year. Germanic origin. - old: From Old English 'eald', meaning aged, ancient. Proto-Germanic origin.