Srimad Bhagavatam Canto 09, Chapter 18, Text 39

SB 9.18.39

matamaha-krtam vatsa
 na trpto visayesv aham
vayasa bhavadiyena
 ramsye katipayah samah
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
My dear son, I am not yet satisfied in my sexual desires. But if you are kind to me, you can take the old age given by your maternal grandfather, and I may take your youth so that I may enjoy life for a few years more.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
This is the nature of lusty desires. In Bhagavad-gita (7.20) it is said, kamais tais tair hrta-jñanah: when one is too attached to sense gratification, he actually loses his sense. The word hrta-jñanah refers to one who has lost his sense. Here is an example: the father shamelessly asked his son to exchange youth for old age. Of course, the entire world is under such illusion. Therefore it is said that everyone is pramattah, or exclusively mad. Nunam pramattah kurute vikarma: when one becomes almost like a madman, he indulges in sex and sense gratification. Sex and sense gratification can be controlled, however, and one achieves perfection when he has no desires for sex. This is possible only when one is fully Krsna conscious.
 
yadavadhi mama cetah krsna-padaravinde
 nava-nava-rasa-dhamany udyatam rantum asit
tadavadhi bata nari-sangame smaryamane
 bhavati mukha-vikarah susthu-nisthivanam ca
 
“Since I have been engaged in the transcendental loving service of Krsna, realizing ever-new pleasure in Him, whenever I think of sex pleasure, I spit at the thought, and my lips curl with distaste.” Sexual desire can be stopped only when one is fully Krsna conscious, and not otherwise. As long as one has desires for sex, one must change his body and transmigrate from one body to another to enjoy sex in different species or forms. But although the forms may differ, the business of sex is the same. Therefore it is said, punah punas carvita-carvananam. Those who are very much attached to sex transmigrate from one body to another, with the same business of “chewing the chewed,” tasting sex enjoyment as a dog, sex enjoyment as a hog, sex enjoyment as a demigod, and so on.