There are many ways to kill yourself and many reasons to do so. When I lived in Livingston County, Michigan, there was this old couple, married a hundred years more or less and she passed away first and a few days after the funeral, he died. No one asked any questions or needed to. His death was ruled "natural causes" and it was close enough. Even a nominally young person could face unremediable prospects of disease, paralysis, overall loss of life quality. Why delay the inevitable as it just gets worse? (Clearly, someone 20 has more likelihood of better outcomes over time than someone 60.