How is this even a question? It is like asking, to what extent are apples a real fruit, or to what extent are Quora writers real people (this question gives me pause to doubt).
Is German a real language? Or Russian? How about English? I’ve been speaking it all my life, but maybe I’m living in the Matrix and it isn’t a real language at all?
Ukrainian, like Polish, Czech, Serbian, and Bulgarian, is a Slavic language, which originated from Proto-Slavic, a hypothetical, scholarly reconstructed language from thousands of years ago. Over time this original Slavic language evolved into three main branches; West Slavic (Polish, Czech, Slovak, etc.), South Slavic (Bulgarian, Serbian, Croatian, etc.), and East Slavic (Ukrainian, Belorussian, Russian).
There is no scholarly consensus as to when the three main Slavic branches diverged, or when the languages within them became separated. One theory argues that within the East Slavic branch, Ukrainian became a separate language in the 8th or 9th century CE. Another theory, favored by Russian and Soviet scholars, claims Ukrainian, Russian, and Belorussian split ways sometime around the 14th century. There is even a theory that Ukrainian actually developed independently directly from Proto-Slavic.
All of them are educated speculation.
The most conservative generally accepted consensus is that Ukrainian existed as a separate language at least 700 years ago.