Even the iron age might be ambitious. I remember this coming up in disucssions during the brief run of the TV show "Revolution" where something turned off all the electricity, and people were scoffing at the very low levels of tech displayed on the show, pointing out all the technology that was better than the show's, but did not rely on electricity. Except there are those techniques we don't have. We don't know how to make iron without electricity. We might know the formula for gunpowder, but not the myriad little skills for mixing it correctly and safely. There's a lot on which we know the theory, like blacksmithing and organic farming and hand-made clothing, but not the practical skills, and even much of our theory depends on support from modern technology. It's one thing to claim you can bake a loaf of bread from scratch, but most people who do that are presuming on the ability to buy flour & yeast, and have an oven with modern technological controls, and wouldn't know what kind of flame to use, or how long it takes to cook the bread properly.

For steam power, the theory is easy, but do you know the tolerances of the parts of a steam engine? Do you know how to make them all fit properly together so there is minimal or no leakage of the steam, when you are doing so without machine tools? Sure, making nails on a forge seems doable, but what about bolts, nuts and screws, which need to fit very closely together?

Old timey people took a long time to invent things, because they had the craftsmanship, but needed to figure out the theory. We are extremely confident in our own potential capacity because we have the theory...but we don't have the craftsmanship.