Words carry baggage, a cloud of associated meaning that extends somewhat beyond what you'll find in the dictionary - and in some cases effectively supersedes the dictionary definition in common usage. Language is a living thing, and dictionaries are the conservative statements of a language's gatekeepers, not its primary and most numerous users.
It recently occurred to me that "rejuvenation" is a word whose primary meaning and baggage in common usage is no longer the first entry in the dictionary.
re·ju·ve·nate: to make young again.
This is important, because when we advocate engineered human longevity by using the word rejuvenation, to make young again is exactly what we mean. We are being precise, and using rejuvenation to mean "a hypothetical reversal of the aging process."
The problem here is that "rejuvenation" has long been a term of art and marketing brand for cosmetics manufacturers, the horrid "anti-aging" marketplace, dermatologists, and plastic surgeons - four communities with a significant overlap. They also boast very significant revenues, meaning their voices are loud and their presence hard to miss.
What all of these groups have in common is that they develop and sell products and services claiming to restore the appearance of youth to some degree: fake rejuvenation, in other words. At best it's a matter of papering over the cracks - but these folk use the term rejuvenation without qualification or reservation. In their eyes and publicity materials, "rejuvenation" means exactly "faking the appearance of rejuvenation."
Here is something I noticed only recently: head on over to PubMed, the reference repository for papers published in scientific journals, and search for "rejuvenation". You'll quickly see page after page of dermatologists and plastic surgeons talking about the tools and techniques by which they fake the appearance of rejuvenation in skin and facial structure. Every technical artifice, none of which do anything to intervene in the actual process of aging, is labeled as rejuvenation - because in their field, rejuvenation means artifice. It means fakery, deception, and alteration of appearance.
As I mentioned, this is a rich field. Throw enough money into marketing and the meanings you ascribe to words will spread into common usage. On the whole, this is a somewhat depressing state of affairs, but par for the course given human nature.