I know what 'dressy' means, and , yes I agree, if I was going somewhere dressy, I wouldn't wear jeans, but then I wouldn't wear anything dressy while going about my ordinary business, Wearing a mother-of-the-bride outfit for doing a the weeks supermarket shop, for example, or having coffee with a friend would look out of place.
But I am at a loss as to what 'ladylike' means, so cannot say whether wearing jeans is ladylike or not, also what has age got to do with it?
The older we are the more varied we are in how we age. I have a tall slim cousin, who was 80 this year. She is one of those people who, even in old age, could look elegant dressed in a black plastic binbag.