You're probably right in that I have a bias. I'm in NH. I'm only an hr from you. And yes, historical society's are pretty stupid. If that's what you were hinting at.
However, if you're using the mean age, then you are including a house that was just built last yr. If you take 1 house that was built yesterday, and average it with a house that was built 150 yrs ago....? The numbers skew themselves in that measurement.
So the more you build now, then the more the numbers are skewed in taking the average/mean down.