There are several points worth noting:
(1) The notion of a 'natural lifespan' is arbitrary in modern society. What is truly 'natural' - in the sense of that which would take place out in the wilderness absent any technological intervention - is for most of us to be dead of parasitic diseases. It is certainly not for most of us to live into the 80s, or even to live long enough to die of heart disease, cancer, and other mainly degenerative conditions. Is it 'natural' to put a cold compress on someone's forehead but 'unnatural' to operate on his brain? Why, or why not?
(2) Tangential to that, it is most certainly 'natural' to the human species to develop and implement technology. It's what we do. It's what we are most suitably evolved to do. Just as a sparrow utilizes flight to extend its lifespan and improve the survival of its progeny, so we use technology to accomplish a similar task.
(3) There is little doubt that indefinite youth (for all practical purposes) is coming. Almost certainly just a matter of when, not if. The 'roadmap' from here to there is rather clear at this point; what is missing is the capability to enact it. Sure, the "when" might be several centuries off, but in the grand scheme of things that is trivial. In the personal scheme of things, that is everything.
(4) There is even less doubt that if and when that becomes actuality, that it will be adopted for all intents universally as swiftly as possible. Every human endeavor is in one sense or another designed with that end in mind: immortality. In time, for our progeny however removed that are born into such a world, it will probably seem perfectly 'natural' - or at least the rightful order of things.
(5) It won't be true immortality in any case. Estimates are that if you eliminate causes of death due to aging and disease the average lifespan would still be only about 800 years or so. That is due to accidents, homicides, suicides, etc. If you eliminate most causes of death that might be deemed psychological (in the presumption that we will also attain the ability to manipulate human psychology to that degree as to make suicide and homicide events of minimal incidence) then you are still looking at an average lifespan of around 1500 at best.
(6) If you beat those odds, there is still another inconvenience that follows, and it's unclear when precisely that would follow: your head can only fit so many neurons. Eventually they will all get imprinted. Without some kind of capacity extension, you will at the very least begin to lose memory of your earlier life. In time, you will remember nothing at all of your earliest centuries. And at the least it will be a progressive condition. It's entirely unclear what other effects this inevitable process might manifest. We can call it neural empathy.
(7) Every aspect of society is designed around the notions of mortality, demographic growth, the centrality of procreation, and the normative stages of life. This would obviously change in a dramatic (and I would say glorious) way in the event that even a century of additional longevity became standard, much less a millennium or more. The magnitude of the subsequent changes is probably a formidable, unnerving, and frightening prospect to many people. Oh well. Life is change. The prospect of industrial civilization is demonstrably a formidable, unnerving, and frightening prospect to aboriginal peoples. It suits us just fine.
(8) If what follows life is oblivion, then you are hardly doing your progeny a favor by 'getting out of their way' when consigning yourself to oblivion, because you are also condemning them to ultimate oblivion as well. So what if you have one or two children (i.e., replacement rate) instead of four? As if that many people in advanced societies have children above replacement rate anyhow.. If we use quantity of life as a proxy for quality, one child that lives 1000 years has beaten nine that live 100.
I am speaking here to the notion of legal or ethical prohibitions on the extension of life. In other words, to a prohibition that would by its nature apply to your progeny as much as to yourself.
(9) If what follows life is something other than oblivion, you will get there surely enough in any event, and once you do it won't likely matter in the grand scheme of things how long it took you to get there. A millennium is not even the twinkle of a quark by comparison to eternity. Well, assuming that what followed would be eternal, which is not guaranteed, but of course the less eternal that would be, the more value there would be to an extended life.. If it makes you feel better, you can think of it as that much more opportunity to repent and find salvation. You can also always kill yourself off.
(10) Inaction is an action. Failing to save life when you can is indirectly murder. If God does not will that it be so, it will not be so. If it is so, God must will that it be so. Our progeny however many generations removed will think this whole debate quaint and silly - if not barbarous and ignorant. If none of this ever comes to pass, there are worse ways to waste time than this idle banter. Well, the same could be said even if it all comes to pass.
Have I missed anything? =)
I can't imagine anyone more talented than you sir to address all of this. In fact, I can't imagine anyone but you addressing any of this to my satisfaction at all. Maybe you can, maybe you can't. But if anyone can, you can. I watch and wait.
Your odds are, via my bullshit math, somewhat better than that. Well, not complete BS, but here goes ;)
Let's assume that we've eliminated all disease as a cause of death. Further assume we've cheated old age via a fountain of youth potion, such that death due to aging is no longer possible either. We are not, of course, immortal as a result - stepping in front of a bus will still do you in, in our brave new world. So we're left with death by some type of injury as the sole remaining cause of death for everyone - accident, suicide, or homicide.
Now, according to the fine folks at the National Safety Council ("You there, safen up!"), your odds of dying from accident or injury were 1 in 1755 in 2002. This means that you had about a 0.06% chance of dying due to misadventure in 2002, or a 99.94% chance of surviving the year - at least as far as injury is concerned. So to go forward, for the sake of convenience let's assume that this rate of 1 in 1755 continues to hold true for the next few millennia or so. Assume a fixed rate of death due to injury, in other words. This is likely to be a big source of BS here - there's no real reason to assume it'll remain the same, but what the hell.
Okay, relying on the false precision of my calculator here, your odds of survival for a given year are 1754/1755, or 0.999430199 (yeah, yeah - and I cut some off, too, but let's not have a significant digits argument here). Extrapolate those odds outward, and what you find is that you hit 50% odds at around 1216 years. In other words, you have a 50% chance of surviving to age 1216, given those odds of death due to injury.
Now, the problem is, that number doesn't really tell us all that much about you or any other given individual - your odds of surviving this year are the same as they were last year, and there's no bookkeeper up there keeping track of the odds steadily accumulating one way or the other for you specifically. But what it does tell us is something about the whole population. Basically, what we have is a fixed rate of attrition - decay, in effect - and what we can do is start thinking in terms of a half-life for the whole population, rather than an average lifespan. So given that fixed rate of decay, 1 in 1755 annually, our half-life as a population should be right around 1216 years.
Okay, the folks at CDC tell me that 4,091,063 live births occurred in 2003 (yeah, I'm mixing years - sue me). Let's assume we applied the magic elixir to them at birth, eliminating any possibility that they'll ever die of disease or "natural causes". Okay, well, we know that, statistically speaking, half of them will be dead by 1216 years of age, but what about the rest? Grinding our way through our half-life calculator, what we find is that after 1500 years, we're still left with about 42.5% of our original population of 4+ million babies. After 2000 years, we're left with about 32% of our original population. Not bad, eh? At 3000 years, we drop to about 18%, and at 5000 years, slightly less than 6% of our original population should still be hanging around, statistically speaking.
Now let's go for it. After 10,000 years, only about 0.33% of our original population will be left - somewhat less than 14,000 people out of the 4+ million we started with. After 15,000 years, we're down to 0.02% of the original population, or fewer than 800 people. After 20,000 years, we drop down to 0.001% of the original population, or fewer than 50 people.
What's it all mean? Well, our elixir would, based on the current rate of death by injury, make it possible to live for a very long time in a few cases. The vast majority of people wouldn't make it that far, but for a lucky few, they would have a lifespan that far exceeded what we currently know as the entire span of recorded human history, which is only about 5000 years so far if you go back to the early Sumerians. Something to ponder with your coffee in the morning ;)
Maybe not, but it appears that Ma has. (Mother Nature, that is.)
It sure seems to me, with all this Evolvin' goin' on, that She would have evoled Eternal Life, instead of all this death and sex and reproducin' and failin' and eggs and live births and.......
SO much simpler theory:
You ALIVE?
Keep at it!