Basic Trope: A woman is over 25 and not yet married, spurring commentary from contemporaries and/or her own anxiety about getting older and less attractive. See also, Old Maid.
Straight: Alice is 25 years old and single, and her parents or friends nag her to choose a man and try to fix her up with Bob, commenting on how she's not getting any younger.
Exaggerated: Alice is 25 years old and single, and miserable to the point of madness. And still receives flack from her parents and friends about her single status.
Downplayed: Alice only gets flack from her mother; everyone else is cool with her single lifestyle.
Justified: Alice is living in some time or place where the average life expectancy isn't all that high and 25 is considered old. And where marriage and Babies Ever After are seen as the only reasonable lifestyle for a respectable woman in that time and place.
Alice is 25 years old, married, and concerned about having married too soon.
Alternatively, Bob is the one who catches flack for being single and over 25.
Alice is 25 and single, but doesn't seem to catch any flack from her friends and family for it, and doesn't seem to have any anxiety about her single status.
Alice is 25 and although not married, is in a long-term relationship with Bob. Hints are dropped that Bob (or even Alice herself) may propose soon.
Alice is younger than 25 and single, but still treated by her friends and/or family as if she were a full-fledged Christmas cake.
Her lack of anxiety about her single status is a facade; her anxieties about getting older/her biological clock/etc. keep her up at night. And her friends and family never bring it up to her face, but discuss her single status behind her back.
Alice is in a long-term relationship with Bob, and just when it seems like he's going to finally pop the question, he dumps her (or she dumps him) for some reason. (Whether good or lousy.)
Parodied: Alice is single, and when she blows out the candles on her 25th birthday cake, she dies instantly of old age, or magically turns into a shriveled and bitter old hag with 100 cats by her side.
Zig Zagged: Alice flip-flops between feeling happy to reap the benefits of being single and unhappy about being single.
Invoked: Alice reaches her 25th birthday with no man to speak of, and becomes depressed, believing that she will turn into the Crazy Cat Lady at midnight.
Defied: Alice is 25 and single, and she chooses to be single. She may be a Straw Feminist, or asexual, or she may not believe in the institution of marriage. Or she may be waiting until her career is established or other goals are achieved before even thinking of husband-hunting. She does not believe that she (or anyone else) *needs* another half to be whole. Whatever the reason(s) for her choice, she is happy with her decision, and does not let others' opinions regarding it get to her.
Discussed: "Alice should really find herself a man before she gets too old."
Conversed: "Why does Alice need a man? She's an awesome character, regardless of her marital/relationship status!"
Deconstructed: Alice is single at 25. But it's not so much her single status that bothers her as the nagging she gets to get married, or her insecurities on the lines of "What if I'm not good enough/pretty enough/what have you?" Or the fact that no one ever seems to bring up the single status of a man of comparable age. Or simply that she feels her biological clock just might be ticking. Or she's concerned about not being able to relate to her girlfriends (all of whom are married or in long-term relationships and/or having children) anymore.
Reconstructed: Alice gets over her hang-ups and lives her single life to its fullest. If and when she finally does find a man, she is with him because she wants to be, not because she believes she needs to be. They have a healthy and fulfilling relationship, as well as being happy and healthy individuals. And even if she doesn't find a man by the conclusion of the series or movie, Alice still leads a happy, fulfilling life, and learns to ignore comments from the Peanut Gallery.
Plotted A Good Waste: Alice is a closet lesbian, which explains why she's not interested in marrying a man and having kids.
Played For Laughs:
Alice gets angry when anyone brings up her single status, which they do, repeatedly. She may even Megaton Punch them for doing so.
Alice spends obsessive amounts of time worrying about her single status and desperately tries (and fails every time) to land the man of her dreams. Hilarity ensues.
Played For Drama: Alice's anxieties listed under "Deconstructed" are played up and drawn out into a soul-searching romantic drama.
You know, you aren't getting any younger, dear. It's high time you returned to the main Christmas Cake page.