To extend ones life for spiritual purpose, such as meditation time....few of us really spend more than a hour or two meditating a day, or such really straightly derected for spiritual purpose.
If one wanted to in that context, one could extend ones lifetime, sleeping but 3 hours a day eating one meal....probably about about 4 times or 400 years if one was to live to be 100. If one was a Milarepa or something close. But I expect none of us here are that.
Spiritual means do seemingly exist to extend ones life. I think there are means of the mind, we can utilize as tools...what you call them or how they exactly operate, what does it matter. Give your mind a rest from active thoughts once in a while and I think you are healthier and perhaps as consequence your life is extended a bit. That could be a example of a means.
Compassionate action, that could be another means to this end.
I think As a youthful human...youthful appearing...I'd say no, that is a fantasy for hollywood.
A grossly distorted appearing thing is what I have heard of and expect would occur. A sharp mind as that is the only necessity for consideration of the spiritual not a youthful appearence. Such a appearence is all ego and as such not sustainable in this fashion to my opinion.
How would someone appear living in a confined cage of sorts, cave, or somesuch, no light no exercise(such a being is beyond prostrations) sitting in meditational posture for years till the legs become stuck in such a position, wasted away, big ugly callluses on their bottoms.....quite ugly that would appear. The mind would be quite beutiful the appearence quite revolting.
ONly in hollywood to my opinion.
Means I think they exist, and have rumor heard of some.
"This order considers that progress can be achieved more rapidly during a single month of self-transformation through terrifying conditions in rough terrain and in "the abode of harmful forces" than through meditating for a period of three years in towns and monasteries"....Takpo Tashi Namgyal.