Forced retirement at 55 is now illegal in most states. It is discriminatory and against the law in most of the modern world. Why? Because it's too young to stop work. This situation is just CX trying to modernise and keep up with current practice.
I do agree that extensions should be offered in HKG only or another 'slot' on the base of the extendee should be created to stop blocking popular bases. That situation is something the AOA should address.