I am creating a fictional universe where humanity's evolution followed a different path that it did in ours (evolution might not be the best word, but bear with me).
Long ago, in said universe's equivalent of what we call the prehistory (i.e. when the first humans started appearing), there was already another intelligent species roaming the planet. This species, who, at the time, had already advanced to a similar point where modern-day humans are (speech, culture, industry, technology, you name it) and decided (for reasons that are beyond the scope of this question) to help the humans (who were little more advanced than cavemen) to develop speech, culture and the rest.
The question here being: how long would it reasonably take before humanity would be able to get from prehistoric level to, say, the Industrial Revolution under this species' guidance? Decades? Centuries? Millennia?
- You may assume that the planet is Earth when it comes to measuring time; 365 days of 24 hours (in layman's terms).
- There is no need to take into account the state of planet Earth in our prehistory; you may assume that the state of the planet at that time was roughly similar to present-day Earth.
- Humans had not encountered this species before, despite living on the same planet. However, humanity was generally not afraid of this species, but would accept their teachings from the first meeting.
- Humans in this universe are otherwise pretty much completely identical to real-world humans; there's good ones and bad ones, smart ones and not-so-smart ones, people that would gladly accept the teachings and those that would not, etc.
- Said species had different vocal chords than humans and could thus not teach humans their own language exactly like they spoke it; it would be either an approximation of their own language or an entirely new language designed specifically for human vocal chords. At this point, I'm inclined more towards the latter, especially because of the next point.
- Another difference between humans and this species meant that their writing system was difficult for humans to read and write fluently, too. They could read/write it when taught, but it would take them longer to read it compared to a writing system aimed at humans and even longer to write, even after they become fluent.
Edit: there seem to some misconceptions going on about the level of humans before this meeting. When I say they had 'no language', I mean they had no structured language with grammatical rules; they could speak among themselves by using sounds such as grunts and such and by using body language. They had some basic tools and could probably create fire already. But they had nothing in the way of culture or civilization.