Laudator Temporis Acti

From Goethe's Faust, Part II, as translated at Underbelly:

Once you reach 30,
You are as good as dead,
It would be best if you were timely killed.

Hat einer dreißig Jahr vorüber,
So ist er schon so gut wie tot,
Am besten wär's, euch zeitig totzuschlagen.

Cf. Dostoyevsky, Notes from Underground (tr. J. Coulson):

I am forty now, and forty years is a lifetime; it is extreme old age. To go on living after forty is unseemly, disgusting, immoral! Who goes on living after forty? Give me a sincere and honest answer! I'll tell you: fools and rogues.

Among certain peoples in ancient times, it was the custom either for the elderly to kill themselves or for their relatives to kill them.

Herodotus 1.216.2 (on the Massagetae, tr. A.D. Godley):

Though they fix no certain term to life, yet when a man is very old all his family meet together and kill him, with beasts of the flock besides, then boil the flesh and feast on it.

Herodotus 3.99.2 (on the Padaei, tr. A.D. Godley):

As for one that has come to old age, they sacrifice him and feast on his flesh; but not many reach this reckoning, for before that everyone who falls ill they kill.

Aelian, Varia Historia 3.37 (tr. N.G. Wilson):

There is a law at Ceos that those who are extremely elderly invite each as if going to a party or to a festival with sacrifices, meet, put on garlands and drink hemlock. This they do when they become aware that they are incapable of performing tasks useful to their country, and that their judgment is by now rather feeble owing to the passing of time.

Aelian, Varia Historia 4.1 (tr. N.G. Wilson):

It was a custom in Sardinia that the children of aged parents beat them to death with clubs and buried them, in the belief that it was wrong for the excessively old to continue living, since the body, suffering through age, had many failings....The Derbiccae kill those who are seventy years of age. They sacrifice the men and strangle the women.