There are no such things as clothes for older people. I am a few months short of 80 and the clothes I wear are not markedly different from the clothes worn by my DD, 50, or DGD, 16. OK, no mini skirts, but jeans, leggings not Dv martins, but fairly clumpy shoes and trainers.
As for online shopping, I am selective. Happily by jumpers and tops from better quality suppliers like Lands End, and Culture Vulture, but otherwise like to try before I buy. That consists of taking opportunities whe they present themselves.
DS and family live in York. If I need any clothes, I make time to visit shops there when visiting. It has an excellent town centre and also excellent out of town shopping.
Similarly, when I visit DD her Sainsbury's has much bigger range of clothing than any of my local branches, so a visit to her, includes a visit to Sainsbury's.
Mind you, my shopping for this summer consists of T shirt and sweat short to go with some trousers DD made me for Christmas, both items bought from Lands End, otherwise everything I had last summer has at least another season in it.