Youth is the only thing worth having when I find that I am growing old I shall kill myself
Excerpt from 'The Picture of Dorian Gray':
"I know, now, that when one loses one's good looks, whatever they may be, one loses everything. Your picture has taught me that. Lord Henry Wotton is perfectly right. Youth is the only thing worth having. When I find that I am growing old, I shall kill myself."
Hallward turned pale and caught his hand. "Dorian! Dorian!" he cried, "don't talk like that. I have never had such a friend as you, and I shall never have such another. You are not jealous of material things, are you? -- you who are finer than any of them!"
"I am jealous of everything whose beauty does not die. I am jealous of the portrait you have painted of me. Why should it keep what I must lose? Every moment that passes takes something from me and gives something to it. Oh, if it were only the other way! If the picture could change, and I could be always what I am now! Why did you paint it? It will mock me some day -- mock me horribly!" The hot tears welled into his eyes; he tore his hand away and, flinging himself on the divan, he buried his face in the cushions, as though he was praying.
We all inevitably age, Dorian does not like the idea of that.