It seems to me that this issue should be/will be decided on the basis of statistical evidence, concerning, mainly, heart problems. (And I know the saying, “there are lies etc……..”). I would guess that the expert witnesses that the CAA will call, will be arguing their case on this basis, as will the witnesses that Ian may use.
There must be a point that, statistically, sudden incapacitation occurs more often over a certain age. There are, of course, many factors governing this issue, regardless of age, but at some point, statistically, there will be an age when above average rates of incapacitation will occur – and this figure should be used as a basis for argument. Whether these statistics should be restricted to pilots is an additional question, but I would guess that the general population is probably a better yardstick, if only because there will be a much greater source of information. And if you argue stress levels are different, I would say it’s the younger pilots who are mostly affected - as they learn from experience!