For all the romance novelists would have us believe, I think there were plenty of women who didn’t marry until they were in their twenties. Even in P&P, Jane must be at least 21, because Lizzie is 20, and there’s certainly not the slightest suggestion that Jane is on the shelf. Similarly, Emma Woodhouse is 21, and while publicly claiming her intent never to marry, obviously considers herself perfectly eligible for some time to come. I think 17 to 25 is probably a more reasonable time frame, maybe even 17-30, depending on how a woman aged individually. In Persuasion, the elder sister Elizabeth had not aged visibly at all at 29, while the second sister Anne, at 27, had faded considerably until the combination of a good sea breeze at Lyme and meeting her former love Cpt. Wentworth revived her good looks. They were both considered fairly eligible, perhaps slightly less so than younger ladies, but by no means unmarriageable.
I’d like to take this opportunity to recommend Jane Austen, Her Life and Letters, which I recently read. Her biography is interesting, but it’s her letters which are the treasure. She really was as intelligent and witty and ironic in real life as she comes across as narrator in her books. We might think that it’s Lizzie who unsparingly lampoons her neighbors and relatives, but you will see from Jane’s letters that she was a very shrewd observer of human nature. It’s a pity that her sister Cassandra destroyed a great many of her letters after Jane’s death, but at least we still have these.
It’s also enlightening that she kept a sort of log of what all her acquaintances thought of each and every one of her novels. People’s opinions were very important to her, and P&P was her favorite child, as well as our favorite novel.
I was thinking about this this morning - even if we give Mary all the faults Lizzie gives her - she can marry a clerk. Mary isn’t hideous, she is just a girl with four uncommonly pretty sisters. She is ‘the most accomplished girl in the neighborhood.’ Her manners aren’t elegant and she isn’t lively, but she doesn’t seem nasty - just a little moralistic, not a huge or uncommon fault in that era (or this one). She is a gentleman’s daughter. She has 1000 pounds, and its likely that Jane and Elizabeth’s share was distributed to Mary and Kitty (their fortunes are pocket change to Bingley and Darcy, but double the fortune’s of the other girls) - so that would be 2000 pounds - not enough to attract a gentleman for fortune alone, but enough to interest a law clerk. It isn’t inconcievable that Bingley and Darcy added to Kitty and her fortunes (I don’t think either of them wants spinster sisters living with them forever). Her uncle owns the law business and has no children, making marriage to his neice a good career move for his law clerk. And her brothers are Mr. Bingley and Mr. Darcy - very well connected men - Mr. Darcy in particular with one uncle who is an Earl and another who is a judge - who could be expected to further his career. Even with the face of an eelpout and the disposition of a moldy dishrag, she is not a bad catch for a clerk, and there isn’t any reason to think she is as bad as that.
Yes, quite right and objective. Austen (or her omniscient narrator who need not correspond exactly to Austen) does give us scenes/comments which do not belong to Lizzie which lead the alert to see that Lizzie doesn’t have the whole picture always. I remember finding those bits to be welcome–the letter describing Lydia’s wedding, for instance–here is the world from a completely “uncontaminated” outside perspective.
Austen’s novels are preeminently character driven–the comment that her characters have lives “independent” of and beyond the novel is compelling. (Contra is Nabokov, who hardheartedly reminds us that even so characters are creatures of the author: “My characters cringe as I come near them with my whip. I have seen a whole avenue of imagined trees losing their leaves at the threat of my passage.”)
I’m surprised Mary would have married a clerk. I would think she would have held out for a clergyman. Maybe she mellowed out over the course of the years and became a little less pompous and elevated in her own mind.
I’d also like to think Darcy someday got a more elevated title than simply “Mr.” He might have become a duke, earl or marquis. An estate like Pemberley just cries out for a titled owner (and his lovely wife, of course).
Bumped.
Too bad they got the top two movies mixed up: 
I’ve only seen the 1940 movie with Greer Garson and Laurence Olivier. In that, Mary is played by Marsha Hunt. She wears glasses, is very bookish, rather nerdish and socially inept. She fancies herself a fine singer and musician and confidently warbles songs off-key. At the end of the movie, Mr. Collins and Mary are playing a duet, she on piano (singing terribly) and he playing the flute.
I’m appalled. #16 and #7 should be swapped! How could they place the 1980 version so low and the then place the 1980 version so high?