The best I can offer is that the earliest carved Christian images are on sarcophagi, at least in the west. There is a beatiful sarcophagus called the “Dogmatic Sarcophagus” or the “Sarcophagus of the Two Testaments” from 320 to 350 AD, which has very clear images of Mary carved into it.
I belive that there are sarcophagi with carved images of Jesus, Mary and Joseph from as early as 250 AD but that is from memory and I could be mistaken.
One of the most spectacular is the
Sarcophagus of Junius Bassus from around 360 AD.
These sarcophagi limit the age of carved Christian art of any kind, at least in the west. Clearly, any carved images of Mary for devotional purposes would be newer.
I do not know about carved Christian artwork in the East. I recall reading about some fresco’s in Syria which picture Mary, dated around the middle of the third century, but again that is from memory and I could be mistaken.
Maybe Patrick will stick his head in the door and give us some information. He is a bit of an art historian and anyone interested might want to send him a PM.
-Tim-