aetas

Aetas, aetatis, f., third declension, contracted from an older aevitas, which is why it belongs with aevum and aeternus rather than with anything to do with annus.

It covers three things English splits apart: how old a person is, the whole span of a life, and a historical era. So nostra aetate is "in our time", not "at our age", and the context has to decide. The genitive of description does most of the work: eius aetatis homo, "a man of that age". Medieval scribes drop the ae to a plain e, which is where the corpus form etatis comes from. English age arrived through French from the same root, and aeon and eternal from its cousin.