Yeah, I agree right up to the “however”. There are days in February when it warms up to 40 F and I feel like wearing shorts and a T-shirt. My gf rolls her eyes, but I ignore that.
This is my case, altho I was never able to grow the long, thick mane I wanted - stoopit genetics. As I’ve gotten older, my crowning glory has gotten finer and thinner, but on the plus side, I’m 68 and have not yet sprouted a gray hair. Still, shorter is so much easier.
Regarding clothes - it’s none of my business what anyone else chooses to wear, but I reserve the right to snark (privately - never to one’s face) about another’s choices. I’m going to assume people dress the way they do because they like the way they look or feel. So squeeze into those leggings that stretch so far, I can see the floral pattern on your underwear if that’s what you like. If short skirts and stilettos with long pointy toes do if for you, have at it. No skin of my nose if you apply makeup with a putty knife.
I expect snarks may be aimed at me at times. I don’t dress according to any fashion dictates, but I do make an effort to cover what needs to be covered. No one needs to see my bra straps or the waistband of my granny panties! 
If someone finds my choices funny, well, happy to entertain ya! And the day I wear jammy pants to the store is the day someone needs to consider shipping me off to Shady Acres, because I’ve obviously lost it at that point.
I guess it depends what you mean by “older” and “young” and “clothes”.
The reality is that as you get older, you tend to get fat, wrinkled, grey hair and other characteristics of old age. So young people clothes (by which I assume the OP means stuff sexually provocative stuff like tight minidresses, belly shirts, “Daisy Duke” style cutoff shorts, so on and so forth, don’t flatter your appearance the same way they did when you were 20. So you end up looking like an old lady trying to look young.
But, if you can pull it off, more power to you.
Oh why should anyone have to do anything because of other people 
It absolutely depends on the specifics. Long hair , for example - are we talking about a woman with long, somewhat naturally colored hair in a simple style , or an 85 year old with long, obviously dyed hair in an elaborate style that requires a half hour with a blow dryer and a curling iron? What kind of mini-skirt or shorts are we talking about - mid-thigh or an inch below the crotch?
I wasn’t thinking sexually provocative. My thoughts were about slim ladies wearing form-fitting and elegant outfits. Nothing trashy or slutty or otherwise unbecoming. Nothing too dressy or flashy, just… nice.
Can older women wear what they want?
Yup.
Depending on what various people wear, I might get a bit of joy in my life from it or not, but like 99% of the time, that’s none of their business, and I damn well better not try to make it their business.
A few weeks back at my mother in law’s funeral, a woman showed up who appeared to be 60-ish but wearing the clothing and makeup of someone half her age. In most cases I wouldn’t have given it a second thought, but it seemed really inappropriate for a funeral (and I wasn’t the only one who thought so).
That’s as short as I will ever go again, because I like to put my hair up with a stick. It’s better and more comfortable than a ponytail even. Like flipping a switch from long hair to no-need-to-think-about-it hair! 
I feel like I should chime in, since the OP mentions that this thread was inspired by my “shorts” thread. But I really have very little concept of fashion whatsoever, hence my asking the “shorts” question, and even less so regarding women’s fashion.
I will say that, in general, I think everybody should dress and manage their general appearance in the way that makes them the most happy and comfortable.
I do lots of things because of other people. Those are things which actually affect the other people.
Telling people, women in particular, that they should dress to please the eyes of strangers has a long and unpleasant history. Only it ain’t history in the sense of past; it’s still very much going on.
– I will grant that I keep clothes on outdoors around the farm to some extent because my Old Order Mennonite neighbors might show up unexpectedly at any moment. They’re the same clothes I’d be wearing most of the time to protect my skin and/or provide pockets, though; so it’s just a matter of not deciding to relax for a few minutes with my shirt off.
What about an 85 year old with short, obviously dyed hair in a style which requires the assistance of a hairdresser, time with a blow dryer and curling iron, and hair spray? Nobody seems to blink at that. What difference does the length of the hair make?
Are you objecting to fat women doing so?
As a general matter, I believe most people look best when they dress within a couple of decades of their chronological age. This works in both directions, and for men as well as women. (A boy/young man rarely looks his best if dressed in clothes most frequently seen on a grandpa - or even a mature middle-aged man).
Take Helen Mirren. An unquestioned knockout in whatever she might wear. But who thinks she would look her best if she shopped at Forever 21?
We have a good friend who was VERY attractive. But I often thought she would look even better if she didn’t wear hip-hugger jeans and such. I got the impression she sorta dressed younger than she might have because she had a daughter in high school. Sure she still looked good, and so long as she was happy, who cares. But there is a point at which women - and men - don’t really benefit from showing more and more skin, and revealing every curve.
I will add that yes, happy and comfortable works well in the privacy in one’s home. But when going out in public it becomes socially considerate to add what I will call not out of place.
One does not have to be socially considerate but I think that it’s, umm, considerate to do so.
I’m no fashionista and I never was. But I pretty much fit in and wear comfortable clothing.
Now an elderly lady dressed nicely, not overdoing it and not wearing that ‘old lady jewelry’ and what’s worse, not doused in overwhelming perfume, is nice to see.
It can be like this web picture but it doesn’t have to be a dress, and this concept can be dressed down to be casual —
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Some women go to short hair because as they age it’s easier for them to take care of. Or because a shorter cut gives more volume to thinning hair. Or because they want to switch up their style. Or because whatever reason they want. NONE of these things takes away from a woman’s femininity and it’s pretty sexist to suggest a woman with short hair is any less feminine than a woman with longer hair, or that anyone “gave” up any femininity just because of their hair.
I don’t see anyone in this thread talking about men giving up their manliness by shaving their heads. Or even suggesting that hair - on the scalp or on the face - is an indicator of manliness.
I’m American, but I’ve heard it a fair bit. Although I think I first heard it from my mother when I was a kid. Maybe it dropped in popularity in the US? Because we don’t eat as much lamb?
I used to have long hair until my 40s when I switched to a slightly longish bob. With covid, I just let it grow and only trim my bangs. It’s gotten quite long, and partly because it’s relatively curly it’s pretty thick. I keep it pulled up in a scrunchy, because when it’s warm there’s nothing that makes me sweat more than long hair down my back. It amazes me to see male athletes who have long hair competing with it down their neck/back.
Sixty-six here. Do I wear sexually provocative clothes? No. It was never a big habit of mine anyway. I am not too old (in my opinion) to wear cute clothes on occasion, such as a knee-length skirt with leggings and boots. My general for-best look these days is what I hope is modestly elegant – a midi skirt with nice clogs and a flattering sweater, for example. I don’t really enjoy looking at other people’s fat rolls encased in spandex (although, hey, their choice), so I don’t inflict mine on others either. Although I am not particularly fat, I’ve gotten somewhat saggy.
My hair has been short for many years. It’s very thick, straight and fine; it quickly works its way out of any band or clip, and the only way to keep it out of my face is to make pigtails out of it. I wore it long through my twenties but practicality won out.
Almost all my waking hours are spent in either breeches, blue jeans, or loose shorts. Dress-up is for special occasions.
Mine is shoulder length, iron gray, white on top and at the sides. After a lifetime of stick-straight, it curls all by itself. There is an annoying wiry patch in the back where my head rests at night. I would like to get it cut short, but it looks so nice now. (and much fuller than it used to be, I was losing hair during the covid and also because of my thyroid)…I wear dresses and leggings. I gave up jeans ages ago, and shorts. In shorts and t-shirts, I look like Spongebob Squarepants, short and wide, a walking square! 
I will still go sleeveless for comfort, IDGAF about my bingo wings or wrinkly arms.
Nope, not at all.
I guess theres a certain point, if a woman is dressing like an average 10 year old, something is wrong. I love black leggings though.
There is no question that healthy young adults, of both sexes, often look best wearing scant clothing, and things that fit tightly. And that older people, with wrinkles and sags, look better with clothing that hides more. And i, personally, look my best in a well-fitted suit. But i am not trying to look my best, at least most of the time. I don’t want to look terrible, of course, but mostly i want comfortable, low-maintenance clothing with lots of pockets.
I really hadn’t realized before this thread that i wasn’t supposed to wear youthful clothing or hairstyles. I find that idea offensive. I guess i have run into it before. A close friend is kinda a trans woman (it’s complicated) and when they first came out, they wore little-girl clothes. Not sexy teen clothes, but the fanciful stuff that delights five year old girls. And some mutual friends said unkind things about it. And i defended them. “Jane didn’t get to wear that when she was five. She should get to enjoy it now.” And I’m glad have was able to do that for a couple of years. Everyone should get a chance to be delighted by their clothing.
I agree with this sentiment. But, always trying to improve my social awareness, is such a statement a form of body shaming?
Not criticizing you at all. Just trying to understand.