"in your first post you postulated that a counterargument would be to not issue medicals to women because they COULD suffer from PMS."
Not really.
I am only saying that if women wouldn't be allowed to fly commercial single pilot ops, this wouldn't be acceptable because the increased risk involved isn't high enough to exclude someone from the aforementioned type of flying.
Now the same principle applies to someone "being too old". If someone aged 60 or more isn't allowed to fly commercial single pilot ops, this wouldn't be acceptable because the possible increased risk involved isn't high enough to exclude someone from conducting the aforementioned type of flying.
Medical standards are all about risk assessment. Some of the medical standards are based on objective grounds, some are based on subjective grounds. Due to anti discrimination laws medical standards regarding age, sex, ethnic groups etcetera need to be based on objective grounds and be justified and proportionate.
I really don't see the difference of accepting the higher risk involved regarding females and the possibly higher risk of someone turning 60.
You are correct that if you possess a medical, you should be allowed to exercise the privileges of the medical certificate. Unfortunately, people are being denied medicals on reasons that might have no or little affect on safety.
I am sure that you would be everything but happy if you were told that you are not allowed to fly commercial single pilot ops because you as someone of the female gender do have a small but measurable increased risk as opposed to men. Why would the 60 year old feel any different, if the possibly increased risk is still small?
You are correct that gender and age "are different issues". However, they have similar legal protection and therefore the same basic principles should apply. It wouldn't be necessary to mention discrimination due to gender at all, since females nor males are illegally discriminated in at least JAR-FCL 3. However, it is so much easier to realise that it is against the purpose of the legislation if you start by applying the basic principle on female vs. male, and then continue on 59 year old vs. 60 year old.