If humans can't yet achieve immortality, the next best thing would be finding a way to slow down or even reverse the process of aging. While there's an entire industry devoted to so-called "anti-aging," the biological truth is that our fate is written in our DNA. Specifically, the end bits which are called telomeres.
These "caps" don't hold the codes for proteins like genes do, so when the telomere gets a bit shorter each time the DNA replicates, no important information is lost. In humans, those telomeres will eventually get too short and coding DNA will start to be lost in the replication process, throwing a major hitch into cell regeneration. If our cells are no longer replicating at the rate they once did, the impact is felt throughout our body — in short, we start getting older and slowing down.
In one of their YouTube videos, MinuteEarth explains the role telomeres play in aging across multiple species — and why some animals, such as the naked mole rat, don't seem to age at all. Despite their wrinkly appearance, naked mole rats produce a special enzyme that rebuilds the telomeres that keeps them young. Or, at the very least somewhat indefinitely middle-aged.
Forever Young (Or, Middle-Aged At Least)
They aren't truly putting a stop to aging, however: the naked mole rat may be able to live longer at a younger age, and they may have the unique ability to evade cancer, but they aren't immortal. In fact, the longer the critters live, the higher their chance of being gobbled up by a predator.
If humans could extend their lives in a similar capacity to the naked mole rat, we may not have to worry about being eaten by something bigger than us — but unlike our perpetually middle-aged, hairless, wrinkly pals, we can and do fall prey to cancer.