But there is a HUGE difference between living a healthy, active, and fulfilling life and holding a public office deciding extremely sensitive and important things that will decide the outcome of someone’s life or the lives of hundreds of millions of people.
What if 50% of people above a certain age have a mental of physical disability(example), then would an age limit be justified? There are probably more 25-30 year olds than 70-80 year olds that are mentally and intellectually sound enough to hold office.