I agree with the points in this blog post:
https://40plusstyle.com/how-to-dress-after-40-and-still-look-hip/
But I also think the overarching message of that post is that the goal is not to look young, it's to look good/stylish. And if you are over 40, trying to look younger is often aging. So wearing tight clothes, chasing trends, trying too look too polished/perfect, buying cheap/ill-fitting items because they are trendy, or conversely buying all very high end items, can all make you look bad. And if you are over 40, looking bad will make you look old because, well, you're getting old.
My favorite looks from that post are on women who look their age, but also look great -- stylish, happy, comfortable in their own skin.