ICAO does not “rule” as such, it makes recommendations which each country can choose to adopt as rules in their airspace.... or not.
Age 65 is one such recommendation. It applies only in the country whose rules explicitly state it. Inconveniently, to us fossils, it also applies if youre simply over flying the airspace of such a country whose rules dictate a maximum age. The complications of rostering cause the over 65s to be dispatched to the glue factory.
A few countries choose to ignore certain inconvenient ICAO recommendations while others enthusiastically add on even more layers of rules, exceptions and complications because they “know best”.