@JTT,
It could easily be used in that sense, of course, especially if one referred to people as "old spinsters"
However to me it indicates simply a woman of marriageable age, who is not married.
And by "marriageable age", I suppose the generally accepted interpretation of that is "childbearing age".
The word is not popular here now, somewhat out of fashion, most single women preferring to be known as just that.