The Ageless: Almost all Federation citizens have implanted microbot hives replacing their spleens which maintain their bodies at peak condition for centuries. The oldest have over a millennium and a half of personal experience with the technology being first introduced on SecLand in the 5th century. The microbots also repair physical trauma, but it’s at most a Healing Factor with no ability to repair major brain trauma.
Well, technically they can but you end up with a mewling adult-sized infant.
The potential loss of this immortality constitutes the main deterrent to “memetic contamination.”