our 1925 duplex was empty when we bought it, State Farm covered it no problem. Our Triplex is 1914 and State Farm wanted too much so we used and Insurance Broker. They found a decent policy for us with Foremost Insurance...(I think that is the company name), the only mishap was that a Foremost Agent drove by the unit and called it "empty" and they dropped us with no notice, at the time it was fully rented so I am not impressed with them thus far. Not sure if they will make good on any claims or will excuse their way out. I am tempted to renew next year for the $600 extra with State Farm. State Farm has always been good to us, we insure our personal property, other rentals, primary residence etc with them.
I've never heard of age or lease requirements, it might be a regional thing...