I understand that we are living longer now days. As a Lawyer told my Grand Parents, "it's possible to live too long". My grandmother actually did as her last five years was in an alzheimer's condition where she didn't know where she was when sitting in her own home, or who most of her family was. Physically she was quite fit for her age.
The reason I mention this is no matter the body we have if we don't have our mental faculties we have nothing and we become someone that someone else has to look after. I understand people in their 50's can be hit with alzheimer's.
To me the end of the line comes when we don't have our mental sensory faculties, physical health, or mobility.
That age will vary with each of us.
From the Book, "The Shawshank Redemption" the character Andy Dufresne, an imprisoned accountant, makes a statement which is now famous. "I guess it comes down a simple choice: Get busy living, or get busy dying."
Meaning to me, do something with your life while you have it, and let death take care of itself....just as birth did.