I will say this one last time. Equating the necessity for certain jobs to require physical fitness with the requirement for other jobs to have mental fitness makes no sense. This does not mean we shouldn’t remove people from their jobs because they are old, but because they are unfit. When there is a strong correlation between fitness and age, such as physical well-being, and a failure to perform your job puts lives on the line, age limits make sense. When there is a much weaker correlation between age and fitness, such as mental acuity, other tools will achieve better results.
All of this is tangential to setting a retirement age. If you as a nation are going to require people to stop working at a specific age, then you as a nation should be willing to guarantee the financial well-being of people over a certain age. If you don’t want to support them, then you shouldn’t mandate they stop being able to support themselves. Currently, about a quarter of the American workforce is over 65. I guarantee a significant number of them aren’t doing it out of preference rather than necessity.