I think the most important thing is looking at the fit.
i think layering a vest with the dress makes it heavier and the pattern is also more severe.
You are not overweight so accentuate your waist and stick to softer patterns
Avoid busy patterns except for soft simple florals like a long floral skirt would be cute
try wearing high wasted wide leg jeans. These are trendy but not too young if they fit well they are classic and comfy.
The tapered leg can look like grandma track suit or pajamas.
when I looked at a photo of my aunties the one who is the eldest by 10 years looked the youngest and so I studied this photo and it definitely boiled down to her style, the fit of her clothes, and how she did her hair.
she also wore a bit of makeup and the other 2 did not wear any. How to do mature make up is a good skill because just a little bit in natural soft colors can do wonders
she had a longer shoulder length style that she styled in a feminine way as opposed to short masculine cut that also looks elderly (she died it blonde but this suited her skin and blue eyes so not sure if blonde is right for you but generally blonde is youthful and flattering for many older women)
she wore form fitting clothes in soft pretty colors and belted jeans that accentuates her waist. ( as opposed to the boxy plain white tops that made the other younger women look fatter and older even though they were not any bigger than her it gave the impression of having a square boxy figure (as opposed to an accentuated waist that is youthful
If you like a slim or tapered leg Go for Gloria Vanderbilt jeans, high waisted with a belt
this was an auntie who was over 60 and she looked so much younger and better than the other 50 year old aunties simple because of a few style tricks and also I think her radiant smile. Having a white smile and smiling more is also youthful. So part of it is energy, so doing energy work (yoga tai chi dance etc) help move the energy upwards and give a youthful impression