Can someone please explain that theme 

Lots of things happened before the release of the original Nintendo Entertainment System (or Nintendo Family Computer/FamiCom in Japan).  Consoles, arcades, pop culture...

How you interpret the theme is entirely up to you, but the idea is to think back before the console that rebooted the games industry.

Okay just to clarify if I get a game like deadly towers released 1986 and modernise it to 2020 standards is it fine 

Or I can only modernise a game made before 1983 when the nes was released 

Thanks in advance