"This glass is ancient."
Translation:Αυτό το ποτήρι είναι αρχαίο.
Oh my, I just realized what you mean. Of course, it's not just a drinking glass. In fact, as you state the idea of it being ancient fits much better with the material rather than the item. We do need to add that version right away. Ah, I see you have added it to the incubator comments. Many thanks.
Well in English, which compared to Greek is the new kid on the block, we use "ancient" for something that occurred 1400-1500 years ago.
For Greek "αρχαίο", we'd have to go back around 2,500 years. The Parthenon in Athens is 2,466 years old. It was constructed between c. 447 BC-432 BC.
Of course, we can use "ancient" and "αρχαίο" metaphorically, as in, "We've got an ancient couch which is very comfortable." "Έχουμε έναν αρχαίο καναπέ που είναι πολύ άνετα."