Shunamitism

Shunamitism (also referred to as gerocomy[1]) is the practice of an old man sleeping with, but not necessarily having sex with, a young virgin to preserve his youth.

[4] When King David was old and could not stay warm, his servants found Abishag to sleep with him, though he had no intimate relations with her: therefore, she was still a virgin.

In the 16th century Chinese medical book Bencao Gangmu by Li Shizhen, it records that "For old man, or humans who lack the energy, sleep with a girl who is before 14, as there is no better medicine than receiving the qi that is present in a young girl", however it advises not to do any sexual acts and just sleep when performing the practice, as it would have a reverse effect if you do.

The book also notes the relatively new variant during the time called "contact for supplementation", which lets the girl send the qi to enter the nose orifices, navel, and essence(sperm) gate, so as to reach their cinnabar fields.

[9] The young girl that was used for the practice was called "witbangagi" (윗방아기) and was usually of slave origin or from a poor economic background and was usually used by the Yangban class.