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according to THE Dictionary of English Idioms & Idiomatic Expressions
the expression AGE BEFORE BEAUTY is used in English language by some one in a way of allowing an older person to do something first, though often in a slightly sarcastic way.
Historically the expression AGE BEFORE BEAUTY started life in the late 19th century probably as a graceful way for an older woman to acknowledge the courtesy of a younger one who stands aside to let her take precedence in entering a room. It soon came to be a gallantry of an older man to a girl, and to be used jocularly and maliciously between other pairs.