Just because a home does not have the age listed it does not mean that the house was built prior to 1930, it just means that they do not have the info at hand.
Sometimes a home seller does not know the age of their home; in this case a little research or local knowledge of the architecture could help establish an approximate age of the home; but not all homes as you know will have their age listed. I have been to many homes of varying ages with their "year built " listed as age "unknown".
Livingston celebrated it's two hundredth year anniversary last month, but the area was fist settled circa 1700. Few very early home survive today and the town did experience a later build out than some of the surrounding towns that were more accessible due to the train lines. Many homes were built between 1940-1960, while surrounding towns experienced a building boom in the mid 20's.
An experienced agent with local knowledge can help guide you through this process, feel free to contact me if you need any assistance.