What decade is truly old?

I mean the 60s-80s were old but they are like retro/vintage old. Not old enough to be considered antique. 

Anything before the 80s seems out there to me.

I agree, the 1950s influence is still impacting today with things like suburb lifestyle, television, teenage culture, modern pop structures, and some of the fashion trends are still being worn today:

1200 BC

in the 1920s? I'm sure that wasn't the case across Europe.

The 1940s if we're referring to the most recent decade to have little to no connections with the present day, but in all seriousness, I really do think that the argument could be made that it's actually the 1980s which is the oldest decade to exert any significant influence on the world today. It was the decade that saw PCs, climate change, and post-modernism all enter the mainstream consciousness, not to mention the fact that '80s nostalgia is still all the rage at the moment. You can find far more parallels between the way in which people went about their lives in the 1980s and the present day than what you can if you were to compare the year 2020 with any era before then.

While that may be stating the obvious on face value, there is in fact quite a number of significant differences between how society functioned before and after the 1980s, not just in terms of technology, but also in relation to general psyche and communication. Portable music listening and mobile communication had become standardised by the 1980s. That's a pretty big deal, in my opinion, seeing as how the basis of streaming (which has been so integral to the way in which entertainment is consumed) itself revolves around being able to listen to whatever you want, when you want. Also, the period of time between the birth of rock 'n roll in the Mid 1950s and the emergence of MTV was marked by constant transition and the breaking down of the archaic social customs/values of the past, such as achieving equality among race and the liberation of women's rights. While society has continued to progress since the '80s, the '80s themselves were more of a consolidation and a reevaluation of the progress/work that had been done in the two decades prior. Even to this day, we are still enjoying the fruits of what was done during the 1960s and 1970s, and you would be hard pressed to find someone who believes that we are in the exact same stage of human history as what we were in during the 1960s. 

The point i'm making is that with the passing of time, we reach a certain threshold point in which despite a number of noted similarities that may exist between the present day and that of the distant past, the origins of those similarities are simply too long ago to be truly applicable with the present day. Society is a continuum. Youth culture will in all likelihood continue to be a thing 50 years from now, but that doesn't mean the 2070s will have tangible connections with the decade in which youth culture first came into existence; the 1950s. The 1950s will be well and truly in the history books by then, even with certain similarities or 'connections' between the two being apparent. Alexander Graham Bell invented the first working telephone in 1876, however, it would be ridiculous to say that we have connections with a time that was almost 150 years ago.