Old people look old not because of their outdated fashion style but because of their age.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.