The
age at which a
woman isn't expected to ever
marry, might start lying about her age, or isn't considered
attractive anymore. What, exactly this age is varies greatly.
"She was twenty-five and looked it, and so there was no longer any need for her to try to be attractive." (Gone With The Wind, describing India Wilkes).
(Note: the author of this write-up is 26 and doesn't consider herself an old maid.)