The most fashionable thing anyone can possibly wear is the least fashionable thing. It's an incredibly potent counter-signal. Haute couture is deliberately, wilfully hideous.
Not anyone, only those lucky enough to have sufficient inherent attractiveness to outshine anything they could put on. When those have established a new aesthetic (either top-down/haute, or bottom-up/street), the industry comes in and skillfully polishes away the rough edges so that the basic idea can also work on the less fortunate, who will then for a brief period be able to enjoy a "pretty by association" halo effect.
Sceptics sometimes consider the fashion lifecycle to be some kind of artificial conspiracy made up by the industry to create demand, but I think it is more an emergent phenomenon of human interaction that could only ever be subdued by extreme scarcity or by draconian regulation (e.g. rules applying to lower classes in many feudal society).
Old people look old not because of their outdated fashion style but because of their age. Kind of obvious, but we really like to forget that, over and over again (maybe to distract us from our own aging). When isolated from the aging payload and put on fresh bodies (sorry for the cynical wording), time-tested styles work remarkably well. On top of that is a short window where the last generation using a given style has just disappeared from the streets enough to to avoid confusion, but memory of wrinkled faces is still fresh enough to make youthfulness stand out by contrast.
I've seen a few young adult females wearing some 90s style retro sportswear alongside with modern clothes (e.g. a Nike retro windbreaker) and I remember I found them (the persons) quite pretty.
If they dressed like theirs, they'd be unfashionably outdated. If they dressed like yours, they're rediscovering new old fashion trends.