So you've just pointed out very effectively how you don't know what you're talking about.
Lolita and gothlic lolita are still very much a thing in Japan, and in some circles are spilling out into the USA. Here's a link with a lot of photos. None of these girls are old, or are dressed old. It's a fashion sect, and its frilly and full of bows and flower patterns out the ass.
Also Ran has worn leggings, stockings, and all manner of things on her legs while also wearing a skirt. Not that it matters. You can't say she is both dressing like an old lady and being "frisky" (which btw is another way of saying slutty), as it is not possible to be both at once in this circumstance. I know for a fact I'm not wearing stockings in the summer, and she wears leggings in the winter a lot of the time. Sonoko is the one who goes bare legged in the winter, usually. Example? When they had that murder at the skating rink with the hunters. Makoto told her to wear pants via text.
Ran has showed a bit of cleavage before. I would go find scans but MangaReader was having a problem with their DC pages all 404'ing, so it would be really difficult. I pay attention to the clothes, okay? I remember thinking, wearing black leggings and using the slippers must feel weird.
If another character is proving a point about how Ran is not dressing oddly/slutty/etc, then they will come up. To dismiss the other character as being off-topic means you really don't want to actually have a discussion and are only grasping at straws to hate on Ran.