What is the earliest film or show whose plot incorporated some process by which super-wealthy/powerful people achieve immortality by continually transferring their mind (and then wealth) into the bodies of (non-consenting) healthy young adults?
Seconds (1966) is an example of this, it's pretty much ripped off in Self/less.
Twilight Zone Season 3 episode 31 "The Trade-Ins," air date April 20 1962. IMDB description:
An elderly couple shop for younger replacement bodies, then resort to desperate measures to cover the cost.
While the couple in the episode is not rich, they are requesting a service you would have to be rich to take advantage of.