Life extension was a technology developed during the years of the Old Empire. It was a very painful process which however dramatically slowed the aging process of a body.
The pain caused during the process was so high that resembled a torture, and the receiver might pass out.
After the fall of the Empire, the technology was somehow forgotten and retained only in the Synchronized Worlds. However it was a lure Omnius offered so that he could ally human spies and traitors with him such as Handon and Yorek Thurr.
Vorian Atreides and Gilbertus Albans were also receivers of life extension. Specifically Vorian received the life extension treatment in his early twenties. By the end of the Butlerian Jihad almost a century later, Vorian is described as appearing to be roughly thirty.
Thousands of years later, human beings learned to use melange to attain the same goal.