The phrase age before beauty indicates that precedence should be given, or deference shown, to an older person; in extended use, it is a humorous invitation to somebody—not necessarily older—to go first when passing through a door, etc. Interestingly, this phrase pays a compliment to the person giving precedence.

The earliest instance that I have found is from the New-Orleans Weekly Delta (New Orleans, Louisiana) of Monday 3^rd June 1850:

The “Republic” newspaper has taken strong administration grounds: but its declarations are not in the most refined taste, and its English is certainly not the King’s. Such terms as “heroic demeanor” may be idiomatic in Tennessee, but not elsewhere; nor will the majority of readers comprehend how high qualities can “give” a man “a career in arms,” or “signalize him in his campaign.” We are glad, however, to learn from the “Republic” that it does not mean to rival the Intelligencer. “Age before beauty,” as the chambermaid said as she made room for the old lady.

In her Hollywood column published in several American newspapers—the following is from the Salt Lake Telegram (Salt Lake City, Utah)—on Friday 14^th October 1938, Sheilah Graham (1904-88), British-born American gossip columnist, attributed to Dorothy Parker (1893-1967), American author and wit, the following anecdote involving Clare Boothe Luce (1903-87), American playwright, diplomat and journalist:

Dorothy Parker tells me of the last time she encountered Playwright Clare Boothe. The two ladies were trying to get out of a doorway at the same time. Clare drew back and cracked, “Age before beauty, Miss Parker.” As Dotty swept out, she turned to the other guests and said, “Pearls before swine.”

In his column On Broadway published in several American newspapers in June 1936, the American gossip columnist Walter Winchell (1897-1972) had already mentioned this anecdote but without naming the woman whom Dorothy Parker talked to—he only referred to her as “a rival wit”.

Since then, this anecdote has often been repeated and modified. For example, according to H. James Potter in the Courier (Waterloo, Iowa) of Sunday 11^th May 2003, Dorothy Parker was addressing Nancy Witcher Langhorne (1879-1964), Viscountess Astor; H. James Potter has first quoted some of the purported exchanges between Lady Astor and the British statesman Winston Churchill (1874-1965):

Another classic of the cynical variety involving the Lady and the prime minister, reports that Lady Astor observed if she were Sir Winston’s wife she’d poison his coffee.
“Madam, if you were my wife, I’d drink it.”
Lady Astor either got around and annoyed a lot of people, or she was just the perfect foil for this type of humor.
In still another story involving her, she arrived at the door of a New York hotel at the same time as dyspeptic poet Dorothy Parker.
“Age before beauty,” Lady Astor said, as she stepped aside.
“Pearls before swine,” Parker spit over her shoulder as she swept into the hotel.