I would be interested to know where they have their aircraft insured, not so much the hulls as the liabilites. Do they operate any international services?
From a pedant point of view he may be looking at the number of cycles each airframe has done, possibly way less than average, due to grounding etc. and just divided that number by the number of aircraft to arrive at a figure that equates to the internationally accepted ten year average, based on the type of flying, just a pedant thought.
If they are insured outside Iran, assuming sanctions allow it, then the underwriters will probably know each airframes age etc.