The present development of means to extend life focuses on obtaining more objective time: lengthening the number of years spent alive and in good health. This is absolutely the right way to go, to my eyes. The most effective path ahead seems to be that of developing new medical technology to address the root causes of degenerative aging. But what about the path not taken? What could be done to extend subjective time spent alive and in good health?
As a topic this has cropped up here and there in the Fight Aging! archives in connection with suppressing the need for sleep. We spend a little more than a third of our lives unconscious and oblivious, as opposed to being up, around, and getting things done. Bypassing the need for sleep would be roughly the same thing as a 33% extension of healthy life from the point of view of subjective time.
Can sleep be removed from the human condition? With sufficiently advanced technology, sure. But at this point in the relentless advance of the life sciences it seems premature to make any statement about the feasibility of permanently removing sleep as a physiological necessity. There are a number of groups interested in short term elimination of the need to sleep, such as various military institutions, but I'm not aware of any researchers interested in permanent sleep suppression, nor do I know whether it is even possible to talk about the plausibility of that goal given the current state of knowledge. A worst case scenario would require near complete reverse engineering of the human brain in order to safely make the required alterations. A more likely scenario would involve gathering a better understanding of sleep physiology over the next 20-30 years and a resulting development of sleep-reducing drugs.
One thought with regard to sleep and subjective time is that eliminating sugars from your diet tends to result in the need for less sleep. If you, equipped with a better diet, an alarm clock, and sufficient willpower to skip your beauty sleep, find that you can get by just fine with an hour less of sleep each night, then you have extended your remaining subjective life span by 6% or so. For the record, that's in the same ballpark of additional time spent conscious as moderate regular exercise or calorie restriction are thought or expected to provide in humans - though of course without the health benefits created by either of those line items.
A 6% swing in life span is a drop in the ocean, of course. That we can do so little reliably is why we need better medical technologies.
Other means to gain more subjective time are probably just as far from implementation as the complete removal of the need to sleep, as they require a near-complete reverse-engineering and recreation of the human brain - but at least a great many more researchers are working on the foundations in this case. Once the human brain is fully reverse-engineered, it will be possible to run minds in machinery or software. Setting aside all of the caveats with regard to this (and there are a lot of them), this brings with it the possibility of running a mind much faster than real time: it's all just a matter of the level of processing power baked into the hardware or dedicated to run the emulation software. If you want more subjective time, just run faster.
Another option, one that also only becomes available with the capacity for substantial modification of the human brain and the physical structures that support it, is for multiple instances of consciousness to operate concurrently and with full real-time awareness of one another, all working within the same mind. So you are fully aware and in full conscious control of, say, (a) reading a book at the same time as (b) working at your job at the same time as (c) talking to a friend, and so on. This seems no less plausible than running one mind rapidly, given the necessary knowledge to recreate a human mind in machinery or software in the first place.
This is all a fair way in the future of course, and thus largely irrelevant to whether or not people in middle age today will have the opportunity to live far longer in good health. The first hurdle to a longer life is these failing bodies of ours - and so the first order of business should be building better medical technologies that can fix those failings.