Most of the negative comments do not come from posters from the UK. I've always thought they lived in another world, but its only another place. Catherine looks fine to me, dresses appropriately and is v British
I think you have probably hit on the difference of opinion. Most of people who complain that Catherine dresses like an old woman want her to dress informally.
Americans tend to dress casually, even for important events. There are people who show up in churches wearing shorts and t-shirts. A few years ago, some members of the U.S. Olympic lacrosse team showed up at the White House wearing flip-flops. That simply would not have happened in the U.K., or pretty much anywhere in Europe or Asia.
We tend to dress more formally in Washington, DC, but even here there are women who are underdressed when they attend important meetings with international delegations. Most of our foreign visitors are not offended because Americans have that reputation, but I think it does impact the women's effectiveness.
In the last 10 years or so, I have noticed that some European women, particularly those in their early 20s have started to dress more casually. But, overall, the European women I interact with dress formally for business meetings.
Catherine is on business when she makes public appearances. Think of what you would wear to an important job interview.
I will concede that some women Catherine's age may choose to wear different colored shoes with some outfits, but it is silly to argue that Catherine's "nose bleed" pumps would suit an old woman. She is also a minimalist when it comes to jewelry. Again, it is silly to argue that old women don't wear jewelry or other accessories. Her nude pumps and minimal accessories have nothing to do with age, it is her personal style.
The classic fashions she wears today will be a little dated in a few years because she does wear trendy clothes, but her look will age much better than the clothes Diana wore in the 80s. Diana was always a fashion icon and was never (or rarely) accused of being boring or dressing older than she was. But I guarantee that in 30 years, Catherine's style now will compare favorably to Diana's style during the 1980s. For proof, see the video below.
https://www.youtube.com/watch?v=3qY1OahhMB8