This is a deep interest of mine so I’ll share what I’ve learned so far. I wish I had the patience to go through all my bookmarks and link the studies rn, maybe later. But short answer, probably forever until something actively kills you

So the development of all animals cell is guided by chemical messenger proteins called cell factors. There are factors that cause cells to divide, factors that cause young stem cells to become one type of cell over another, a controlled demolition factor that tells the cell when to die, there’s a factor for everything. There are dozens of these proteins that can affect every cell, and every different type of cell has it’s own normal levels of them. You can think of factors as being like the hormone profile of the cell.

In 2006, a lab in Japan mapped all these cell factors out and discovered that there are four “master switch” factors whose levels can control all the rest. These are the Yamanaka factors, the fucking power runes of cellular reprogramming. Oct4, Sox2, Klf4, and c-Myc, abbreviated as OSKM. By raising the level of these four meta control proteins, they were able to turn adult cells back into stem cells that were identical to the fetal variety. The discovery of the Yamanaka factors rocked the stem cell world and also marked the discovery of manufactured stem cells that don’t need to be harvested from a donor, an insane leap from sticking a big syringe in your femur to get at the stem cells in your marrow.

So over the next decade or so, processes to manufacture stem cells are refined and medical experiments for treating tissue injuries and diseases take place. They also discover how to turn one cell type into another. But around the end of last decade they discovered something else: They took a close before/after look at the DNA of the cells they were converting, and discovered that the Yamanaka treatments were actually reversing all damage. Natural aging involves damage to DNA sections by things like the radiation, methylation or posphorolization of the little cross-beam inside the double helix, essentially their data becomes inaccessible. The OSKM experiments were reversing all of that, and even reversing the shortening of telomeres, which are the little shoelace things at the end of your DNA that shorten with division until the DNA can no longer be reproduced.

Okay, that’s pretty cool, but obviously doing that to yourself would kill you, your body would melt into a very youthful embryonic sludge. You need some way to control the process so you get the benefits without reverting into a giant blastocyst. So scientists got to work on it, and I don’t remember who it was that discovered this next part, but here’s what they found: You can “lightly cook” a cell in the four factors, two rotations of five days on, two days off, until it gets soft, youthful and wobbly without quite forgetting it’s identity. Like putting your cells in a strong sauna to limber up. This treatment is called partial reprogramming, removes thirty years of biological aging with each pass, and can be repeated as soon as the cells have firmed up a bit.

Right now the catch as I understand it is that the petri dishes full of grown cell cultures they tried this on all revert back to their chronological age after a few weeks, but I’m optimistic about this being a temporary obstacle. For one thing, we have no idea how the self-sustaining system of an actual body will react to the regeneration treatment compared to a cellular monoculture in a dish, but it seems reasonable to assume the answer will be “better”. For another, it just means we need to investigate the mechanics of these things: the better we understand the process by which these gains are lost, the better the chance we find a way of locking them in. As for the cancer thing, proper cellular regeneration precludes it’s basis and new insane treatments are getting developed every day. It’s a fully surmountable obstacle IMO.

Whenever I encounter some bullshit meant to demoralize me I simply remember that both Communism and eternal youth are actually, physically possible in this life.

I am also working on a sci fi thing about exactly that lmao

A recent study shows it maybe capped at 156 years; due to neurons in the brain accumulating mutations, other organ’s like the liver could theoretically last for millennia

Study link: Somatic mutations impose an entropic upper bound on human lifespan

news article link

Difficult question, because what is aging in the first place? Is it the shortening of Telomeres? Inflamation? Oxidative stress? Is it just the accrued damage to our systems over time? We still aren’t totally sure. It is a mixture of things most likely.

But lets say science solves all that. What stops someone from living forever? Three things: Accidents, disease, and cancer. Pure dice rolls, but the longer you exist, the more those dice get rolled. Cancer especially is nearly inescapable as you age. So I would agree with other commenters, the best bet is probably a little more than the maximum lifespan now, 120ish.

I don’t think there’s an upper bound beyond probability. Once your brain stops that’s probably all she wrote, and the longer you live the closer the probability of a lethal accident creeps towards 100%. But I also think that we’re further away from solving aging/cancer than we are from fusion power, colonizing Mars, etc because it’s not strictly an engineering problem, it’s an infinitely more complex process problem. You need to have a medical process for every aspect of aging that is infinitely flexible to adapt to any combination of genetics/epigenetics and remain effective, people are too complex for there to ever be just one thing you do to everyone that solves all of their problems - even in cancer treatments and stuff like that that exists today, we have multiple competing treatments for every single thing because you’ll try one treatment on a person and it will do absolutely nothing and then try a different treatment and it will work flawlessly and we can’t pin down why that is in a lot of cases.

Repair of the organism and survival of the personality are separate issues. Even if you have an immortal body, how long will you survive? Provided infinite bodies, how long can you maintain coherency? How do we define one’s conceptual core?

But for organisms, at a contemporary lifestyle it would be destroyed in a freak accident within a few millennia.

I don’t think we have any upper bounds tbh. With all aging research, specially around finding the actual mechanisms of aging, it seems it is just something we can and will be able to stop and even reverse.

Then for the disease that can take quality of life away, nothing indicates most of them are not treatable or curable.

Then there’s organ cloning, robotics and cybernetics etc.

So really, even without crazy unscientific ideas, humans could theoretically live forever.

There’s a PBS Eons episode about aging that’s nifty.

There’s potentially a lot of genetic traits or bioengineering you could do to extend out aging by quite a bit like all the other comments listed.

Even beyond animals though, in botany the concept of life-span and aging is surprisingly flexible due to how the body plans of plants work. You have plants that live only a year so they can dump all their energy into seeds. You have trees that live for thousands of years growing so so so slow. You have plants in harsh conditions that live on and off as just their roots with occasional blooming into “full” plants before they die back again.

My favorite though is plants that grow clonally from rhizomes or creepers or via pupping. An agave, for example, will die after it blooms but it also produces multiple clones along the base of its crown that will just use the old root system. With that in mind, did it really even die? Sort of seems like it just lost a stem and made 5 new ones. That doesn’t work with animals that have organs and a definite shape though. Plants are sort of just stem, leaf root and flower tissue repeated over and over in different places so it’s whatever.

It’d be cool to have a sci-fi concept where an old body can be induced to grow a new one while copying over the brain biologically neuron for neuron. Like you throw someone in a pod in a coma for a few months and a fetus starts to form attached to them while their old self shrivels away until they have a new body that’s biologically 21. Once they get out their old body is attached to an umbilical chord and is about the size shape and color of a rock of coal or something freaky.

There’s SOOOOO much that could go wrong with that mechanically or ethically too.

Depends on how sci fi you’re going. A brain transplant into a clone will fix almost everything, and that could be achieved within 50 years if society had its priorities straight (I will not be providing estimates under society as it exists). So like, until brain cancer or dementia gets you, maybe a few hundred years, obviously less if you get one of those early.

Past that, you’d need a way to replace a brain and that’s, well, physically possible because dualism isn’t real, but nobody knows how to do that, we don’t even know the steps to take to research how to do that.

Probably about 110

Depends on how SciFi you want to go. Probably 120 realistically, but if you were to stop or even reverse aging, then it’s all based on the probability of accidental death due to external factors. So, it could be thousands of years.

Star Trek seems a decent guide for less invasive medical intervention. 200-500 years seems reasonable. Being alive is to be deteriorating due to a number of factors, but with enough control and prevention, you could get up there. I think the human mind and brain living beyond 200 would run into some other issues personally, but the physical vessel could be maintained in various ways within the realm of plausible sci-fi.

Even with a reasonably healthy body and brain, I just think people would eventually decided to call it quits at some point though. Aging and death are very human experiences, so departing from that process would be a significant evolution of what being human means. That could be interesting to explore.

Between 110 and 120

I think there are various mechanical questions - maintenance of organs, etc, to perform well for a long period. That’s cancer, disease, replacement, cloned thingies, implants, etc. There are some very old organisms on Earth, so at least from that there’s a good few hundred years.

Then there’s the brain itself. It may not be the “most important” organ per-se, but it’s the one that most directly creates our consciousness and stores our experiences. Regeneration of neurons, removal of plaques, prevention of blood clots… another mechanical problem, if a bit more delicate.

Finally, though, the really hard part. The mind, a product of the brain that isn’t so directly manipulable. The limit of organic human memory storage, the effects of extreme age on skill acquisition or thought bleedover or dreaming… these have a material basis, but the knock-on effects of attempting to, say, augment memory storage and recall, could have very subtle yet negative effects on the Human. Different treatments might have dramatically different psychological effects. I think you’d need a very long period of time to actually work out the kinks in any longevity-oriented mental alteration. And even solving all those so the processes can continue as-good-as-ever - the way they then combine to create consciousness just might not be stable when the number goes up too far, regardless of their individual longevity.

Vernor Vinge did a near-future novel called Rainbow’s End, about a famous poet who emerged from severe Alzheimer’s when a novel nanotech repair process was developed, only to have lost his poetic sensibilities - replaced with an impressive mathematical ability (the nanotech essentially just guessing how the damage should be repaired). Life extension, absolutely, but also a massive chunk of selfhood just ripped out and replaced.

Consciousness transfer as a possibility? Biomechanical bodies or organs? I mean with current interventions and luck I’d say a potential of 130.