I am in my 70s, and nothing, but nothing would persuade me to shop in a 65+ dress shop, full of age appropriate clothing. It is my idea of hell.
I never have any problems finding clothes I like in the usual High Street stores. Where do I shop? Monsoon, Next, New Look, Sainsbury's, Lands End (the only company with trousers that fit me), very occasionally M&S, but only for dull things like black jeggings, BHS. I like my underwear frivolous and lacy, loathe polyester, cold in winter, sweaty and smelly in summer. I like clothes to be colourful. I have just bought a bright orange sweater in Next for this winter and cherry red short boots with a kitten heel in M&S. Not all older women put on weight or if they do they get rid of it so many of us can still get into sizes 10 - 14.
I get 'age appropriate' clothing brochures in the post and they drop out of newspapers, never seen anything in any of them that didn't make me shudder.
Why are you treating older women as something other? We are perfectly ordinary people who have been round for a bit longer than most but our tastes in clothes, food, home décor and everything else are the same as everybody else. People of all ages have widely differing tastes and there is no more variation in clothing tastes between older and younger people than there are between a group of people of the same age.
Please, please, please get real. Talk to real older women in the street. The ones dress smartly, with a stylish hairdo and make up, you probably wouldn't realise what their age is. What is your image of a woman over 65? I suspect it is very different from reality.