I fully understand what you say about the loneliness and pain so often associated with aging. But I don't think I would choose a specific age for when I thik it would be time for my life to be over. I just don't want to outlive my health, both physical and mental. Nor do I want to outlive my ability to be independent.
Right now in my early 70's I am doing ok, but who knows what the future will bring. But you know, if I followed your age suggestion, I would only have about 4 years left! Again, as long as my health and ability to live independently goes, I'm hoping for some more years!