I remember reading David Niven’s wonderful autobiography The Moon’s A Balloon, back when I were but a callow yoof, and being saddened by Niven’s story about the brilliant actor George Sanders.
Sanders declared that at age 70 he would commit suicide, because “my cock will have stopped working, my memory will be fading and all the joy will have gone from my life.” And he was true to his word.
The above was sparked by reading this article:
The Kessler twins — a German entertainment duo who became famous both in the US and throughout Europe beginning in the 1950s — have died at 89 after choosing to end their lives together.
The singing and dancing sisters reportedly died together in their home in Grünwald, near Munich.
The Kessler twins once were known for making the rounds on American talk shows and performing with multi-hyphenate entertainment giants, including Frank Sinatra, Fred Astaire and Sammy Davis Jr., among other stars.
Apparently, the sisters ‘no longer wanted to live’ and ‘had chosen to end their lives together.’
Here they are back then:

As I said, back in my youth I would not have understood that feeling, that life had passed and now needed to end.
Now, on my 71st birthday, I can understand that feeling a whole lot better.
Before anyone starts reading something else into that statement, let me assure you all that there’s no cause for alarm. My health is excellent — not just for a septuagenarian, but for a man of any age, my doctor reassures me — and I still have some unfinished business on Ye Olde Bucquette Lystte (patience, Salma). Please do not concern yourselves.
I truly understand how George Sanders and the Kessler sisters felt — but I don’t feel that way for myself.
We can revisit this topic, however, when I turn 90.