Wiktionary
way back when
n. (context idiomatic English) A time in the distant past.
Usage examples of "way back when".
In her eyes, way back when, when we first met, you were as culpable for the Commander's trial and exile as Jim Kirk was.
But Federation interest in this world started way back when scientists discovered how argea could be used to keep the human heart and spleen healthy.
It doesn't count our great-uncle Ferdinand, our great-grandfather Ferdinand, or the original Isabella's husband Ferdinand of Aragon, way back when they caused all these problems with the up-timers to start with by sending Columbus off to America.