Quotations about:
    lifetime

Aristotle says that on the banks of the River Hypanis, which falls into the Euxine from a part of Europe, there is an order of beasties (creatures, insects, bestiolæ), which live one day. Of these, therefore, any that dies at the eight hour has died at an advanced age, but any that dies at sunset, in positive senility, especially if it be the solstice. Compare, now, our longest life with eternity, and we shall be found to be in much the same category as these ephemerals.

[Apud Hypanim fluvium, qui ab Europae parte in Pontum influit, Aristoteles ait bestiolas quasdam nasci, quae unum diem vivant. Ex his igitur hora VIII quae mortua est, provecta aetate mortua est; quae vero occidente sole, decrepita, eo magis, si etiam solstitiali die. Confer nostram longissimam aetatem cum aeternitate: in eadem propemodum brevitate qua illae bestiolae reperiemur.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Tusculan Disputations [Tusculanae Disputationes], Book 1, ch. 39 (1.39) / sec. 94 (45 BC) [tr. Black (1889)]
    (Source)

The reference is to Aristotle, History of Animals, 5.19 (552b.18). (Source (Latin)). Alternate translations:

By the mouth of the Hypanis, which on the side of Europe, falleth into the Black Sea; Aristotle reports certain Insects to be bred, that live but one day. Such therefore, of these, as dye at two in the Afternoon, dye elderly; but such, as at Sunset, very aged; and the more, if it be on the longest day in Summer. Compare our life, at longest, with Eternity; we shall be found, in a manner, as short-liv'd as are these Insects.
[tr. Wase (1643)]

Aristotle saith, there is a kind of insect, near the river Hypanis;, which runs from a certain part of Europe, into the Pontus, whose life consists but of one day; those that die at the eighth hour, die in full age; those who die when the sun sets, very old, especially when the days are at the longest. Compare our l9ongest age with eternity, and we shall be found as short-lived as those little animals.
[tr. Main (1824)]

At the river Hypanis, which flows into the Euxine, from a part of Europe, certain little insects, Aristotle says, are born to live but a day. Then, one of these, that dies at two afternoon, dies well-advanced in life; but he that dies at sunset, especially about the summer solstice, decrepit. Compare our longest age with eternity; we shall be found in much the same brevity with these little insects.
[tr. Otis (1839)]

On the River Hypanis, which flows from some part of Europe into the Euxine Sea, Aristotle says that there is a certain species of insects that live only a day. One of them that died at the eighth hour of the day would have died at an advanced age; one of them that died at sunset, especially at the summer solstice, would have been decrepit. If we compare our life with eternity, we shall find ourselves of almost as brief a being as those insects.
[tr. Peabody (1886)]

By the river Hypanis which flows into the Black Sea on the European side, Aristotle says some tiny creatures are born which live for one day. So of these one which has died in the eight hour has died at an advanced age; one which has died at sunset is senile, all the more if it dies at the summer solstice. Compare the longest human life with eternity; we shall turn out to be almost as short-lived as these tiny creatures.
[tr. Douglas (1985)]

Aristotle reports that along the river Hypanis, which flows into Pontus from Europe, tiny creatures are born that live but a single day. If they die at the eighth hour they're of an advanced age, if at sunset, they're decrepit -- even more so on the solstice. Measure the longest human lifespan against eternity: you'll find we live about as briefly as those little creatures do.
[tr. Habinek (1996)]

On the river Hypanis which flows from part of Europe into the Black Sea, Aristotle says that little creates are born which live for a single day. One of them, therefore, that has died at the eighth hour of the day has died at an advanced age; one that has died at sunset is senile, and all the more so if this occurs at the summer solstice. Compare our longest lifetime with eternity: we shall be found to be virtually as short-lived as those little creatures.
[tr. Davie (2017)]

Aristotle says that certain little beasts which live for only one day are born near the Hypanis, which flows from part of Europe into the Black Sea. One of these who dies at sunrise dies as a youth; one who dies at noon has already achieved an advanced age; but one who departs at the setting of the sun dies old, especially if it is the solstice. Compare the entirety of our life with eternity, and we will be found to exist for just as short a time as that animal.
[tr. @sentantiq (2019), quoting from Petrarch, Secretum 3.17]