Death and Cupid got their quivers mixed up, which meant Death was shooting love's arrows into old people, while Cupid was shooting death's arrows into young people, causing them to die before their time.
Cupid realized what was happening, so he went to Death in order to correct the error.
"We need to fix this!" Cupid said to Death.
They did their best to sort the arrows properly, although some of Death's arrows remained in Cupid's quiver and vice versa.
As a result, you sometimes see old people fall victim to Cupid, while some young people fall victim to Death.
Inspired by: Mille Fabulae et Una, a collection of Latin fables that I've edited, free to read online. I am not translating the Latin here; instead, I am just telling a 100-word version of the fable.
Notes: This is fable 815 in the book, which is not in Perry's catalog, although it does appear in Barlow's Aesop, among others.