One thing I wanted to add is that Lydia jokes about how "Jane will be quite an old maid soon, I declare" when Jane is only 23! Of course, Lydia's a silly thing and doubtless exaggerating, but the fact that she does make such a joke indicates that there is a foundation for her to exaggerate on, so to speak. Also, Anne Elliot seems considered a spinster by everyone, including herself, and she is also 27 - and she has much more fortune than Charlotte, at least in theory. Also I believe that in real life, James Austen's wife was 32 when they married, and she was a good catch financially - she took him because she was considered to be on the shelf.