Let's see house built in 1930s, typically small rooms, many dividers. Small closets. Small bath areas. No master bath. Basements are not useable for anything but storage.
House built in 1985 - typicall a 1 story. Larger rooms, larger closets. Typically a master bath area and larger bath area. Basement areas can be finished into additional living area.
How much remodeling have they done? Did they strip the house to the studs with new mechanicals, new room placement, etc? Or did they put in new floor coverings, new cupboards, new countertops?
I typically use a combination of age, but then I don't usually end up with 9 sales in the past 6 months. I don't really use effective age as an adjustment, but do consider condition a predominant value indicator. When a large difference in age exists, i.e., 20-30 year old versus 90 year old, I do make age adjustments, I start with $100 per year and go up after I see what the market seems to be saying . . .