Surely you mean "classic" rather than old?
Hippy?
The first generation of a post-war era. They witnessed regeneration and investment in infrastructure not seen in the UK (since the Roman visit 2000 years before). New social housing created on an industrial scale, new towns and new manufacturing built to support the increase in commerce. A time when young people thought the world a great place, where social migration was easily achieved by those who wanted it. Jobs a plenty. Government money providing a world-leading health service that was free to those that needed it most. If ever there was a point when Utopia was within sight, it was then.
In the mid-sixties, science and fashion forecasters thought we'd all be wearing lycra based catsuits that showed off our perfectly formed slim/fit bodies, results of better eating and moderate exercise. Both results of the anticipated continued increases in the 'quality of living'. The forecasters did not anticipate personal entertainment centres (phones/tablets/video consoles) that would keep the populace hooked to their wifi connection, nor the advent of cheap easily available fat-foods. This two-part combination keeping the would-be lithe millennials, too fat for lycra catsuits to be anything other than unattractive.
My 'fav' period during the last century, would be the late 40's early 50's. Everyone skinny (unless you worked in a canteen or a butchers). Women in long tight pencil skirts, heels, nipped in waist with wide belt, tight blouse with pointed bits, heavy eyeliner, and red-lipstick.
I think I need to lie down .....
And an image by the greatest fashion photographer ever: John French.