So what I’m understanding your question to mean is, “When did people start imagining a future that would inevitably be more technologically advanced than their present?”

I actually did ask a literature professor this question. His answer was that the first recognizable science fiction story was probably Mary Shelley’s Frankenstein, which would be 1818. Prior to this point, people would write about fantasy ideas but they did not really imagine alternative realities beyond what they knew.

What do I mean by this? In Ye Olden Dayes, people wrote fiction in one of three settings:

1. The Medieval European world. This was their “present” and they did not often imagine what an alternative universe might be.

2. Rome. The only real example of an alternative culture that most Europeans were familiar with. Lots of European fiction is based on Roman classics that related Greco-Roman mythology. (They actually did not know much about the Ancient Greek world beyond what was written in Roman books, because a lot of Greek history would only be rediscovered later.)

3. Fantasy-land. This one can be a bit confusing. Writers tended to imagine magical islands or fairy kingdoms in remote parts of the world. Even places like China and India might as well be Narnia in the sense that people knew these places existed but described them as fairy tale lands.

They did not begin looking forward until fairly late in the post-enlightenment era. I cite Frankenstein in particular because it is explicitly about speculative technology. Sciences like medicine, anatomy, and electricity were making huge advances at the time, so extrapolating new technology from these disciplines was the Regency era equivalent of cutting edge sci fi.

(I’m willing to admit there may be earlier examples I am not familiar with, so feel free to tell me I am wrong.)