Worldbuilding

Assuming here that longer lifespan also means slower birthrate, I can see two sides to this argument:

• Development would be slower because there's less turnover over time, and fresh eyes aren't looking at the same problems.
• Development would be faster because a single person could build on centuries of experience rather than having to train newcomers.

How have you approached this problem in your own projects?

I've gone with the second option in my own setting. A yinrih reaches maturity at around 53 Earth years, and lives for over 7 centuries on average. I've stated elsewhere that they achieve spaceflight 5000 years after gaining sapience, which if you scale that to a human lifespan would be like H. sapiens going from crudely knapped flint hand axes to orbital flight in 500 years.

In the yinrih's case, there was no ice age to impede the invention of agriculture, and they unlocked writing at the start of the game, so to speak, instead of having to spend science points to invent it.

But most of all, they were hyperfocused on getting to the stars before even knowing what exactly the stars were, so they spent a lot of collective energy answering a lot of questions. What are the stars? If other sophonts dwell among the stars, and we ourselves are sophonts, does that mean we have our own star? Is that what that hot light in the daytime sky is? Why is there a round shadow cast on the ring on summer nights? Does that mean the earth we stand on is round?