The verb mamy would have me translate as "which century do we have ?", which seems very different from "what century is it?"
It's important to remember that languages are about semantics. One-to-one translations aren't perfect, so you should be translating ideas rather than exact words.
True, you need to be careful with certain expressions. Similarly, Polish people wouldn't tell they "are X years old". They say they "have X years".
you dont say. many cases in this lession are 1-1 translate. and now they are like "semantics" what with "making" and "cooking" since both of them are have same usage in the sentence.
If I understand correctly... "Który mamy wiek?" and "Jaki to wiek" are nearly the same questions for exactly the same answer!?
"epoka" is feminine, so that's "Którą mamy epokę?". But well, that's a lot bigger than a century ;)