nidan verb (upper class) with 'ru' ending (archaic), intransitive verb
Archaic intransitive verb. In modern Japanese, the concept is expressed by 古くなる or 老いる. This form appears only in classical texts.
古典では「旧る」は「ふる」と読み、年を取る意味で使われた。
In classical texts, 旧る is read as ふる and was used to mean 'to grow old'.
The verb ふる is the classical form from which modern words like 古い (ふるい, 'old') and 古す (ふるす, 'to make old') derive. Its exact origin is uncertain, but it is native Japanese.