There’s no mystery. The actual age of a property is the chronological age of a property. Say a house was built two decades ago. That house’s actual age is 20 years old.
The counterpart to it is the Effective Age, which refers to the state the property is currently in.
So, do you know how sometimes you see a person that looks really young – effective age - and you’re amazed that he/she is actually much older – actual age - than what you’d thought? That can happen in the real estate world as well if the homeowner has done a good job with maintenance and renovations.
Usually, this relation of one versus the other comes up in bad scenarios, where the Fair Market Value of the property is brought down because the effective age of the house is much older than the actual age. But in rare cases it can bring the fair market value up because the former is so much older than the latter that it creates a perception of value due to the fact that it stood the test of time and became almost a relic in comparison to other properties in the market.