Older people should be given precedence over the younger and, by implication, more beautiful. This is normally used jocularly, often by the older person in order to flatter the younger.
The origin of this expression is unknown. It was certainly in use by the mid Victorian period; it is recorded in print from at least as early as 1869 (in the Decatur Republican newspaper) and is probably significantly earlier than that.
The phrase is often given as part of a supposed exchange between the U.S. writer, politician and diplomat Clare Booth Brokow, who later became Clare Boothe Luce, and Dorothy Parker. It is said that, in the archetypal circumstances for uttering the phrase, that is, while holding a door open for Parker, Brokow said “Age before beauty”. Parker’s reply was “Pearls before swine”.
Luce later denied the story and doubts about the veracity of the exchange are strengthened by other reports that ascribe it to other participants. Some of the numerous alternative comebacks to ‘age before beauty’ are ‘dust before the broom’ and ‘Beauty was a horse’.
Compelling evidence may be lacking but the ‘pearls before swine’ quip is certainly in Parker’s style. Mrs. Robert Benchley’s biography of her husband includes this claim:
“I was right there, the time in the Algonquin, when ‘some little chorus girl’ and Dottie [Parker] were going into the dining room and the girl stepped back and said, ‘Age before beauty,’ and Dottie said very quickly, ‘Pearls before swine.’ I was right there when she said it.”