The fountain of youth is real and it was brought into this planet by an alien life form. The way it works is that the water it contains allows for cell regeneration in ways that are still unimaginable by human modern science. This is the same technology we have been using for centuries to rejuvenate our bodies, but we cannot allow humans to have access to it just yet. The fountain is hidden and we only allow a very select group of humans to consume this water.
Those who are allowed to do this have been extremely useful humans that have contributed greatly to the enhancement of the world. We are not going to let the general population have access to this, but eventually humanity will probably figure out how to make cell regeneration into something simple that will be available to everyone. It will then completely bury plastic surgery as a career.