I never use effective age in reports -- the entire concept makes my head hurt, and it's much easier to list the actual age, with effective age differences between the subject and comps considered as condition adjustments.
In response to requests for effective age adjustments, I add comments something like this:
In reports where all the comparables are older homes:
"The actual age of the properties is listed in the comparable grid. The subject and all comparables are older homes, with varying degrees of updating and deferred maintenence. For the purpose of this report, all age related differences between the subject and comparables were made as condition adjustments."
In reports with a mix of older and newer properties:
"The actual age of the properties is listed in the comparable grid. With the exception of newer comparables, no age adjustments were made; all other age related differences between the subject and comparables were made as condition adjustments."
I've never been able to wrap my brain around the concept of effective age, and have found it easier to adjust for differences in market appeal on the condition line. When I took the 2-4 Unit Income Property class, the instructor (a long time member of the CO BOREA Board) made the case that effective age is a function of condition, and it's easier to determine and adjust for condition. He convinced me, and when I've included some variation of the comments cited above, I've never had a problem.