Horace is telling his rich friend Grosphus about the things that money cannot buy: peace of mind is the main one, but he also reminds Grosphus that exemption from ageing and death is not for sale either. The example he uses of age is the myth of Tithonus. He was a beautiful youth with whom Eos, winged goddess of the dawn, fell in love. He was a mortal, but Eos successfully begged the Gods to grant him immortality. They did, but, unfortunately, she forgot also to ask for eternal youth, meaning that Tithonus’s fate was to grow ever older and older, but never to die.
Hear Horace’s Latin and follow in English here.