I guess that you are missing the point. We cannot be eternally young while being the same human beings that we are now. As one gets old, memories and experiences change our view of things. When thinking about things like bitcoin today, I cannot avoid recalling what I read and thought of nuclear power, space exploration, nulear fusion, artificlal inteligence, etc, over the past 50 years, and what happened to them. Those memories and the conclusions that I got out of them are what make me today. But it is also the past memories and experiences that make old people more cynical, careless, less enthusiastic, less focused, etc. -- even if the intelligene and clarity of memory remain the same.
So, what does it mean to "be eternally young" --- erase one's memories, and be forever enthusiastic and naive and inexperient as a 20 year old? Or keep piling up memories for centuries, and becoming every time more bored and cynical, thinking more and more about the past rather than the future, etc? Or modifying the brain in some way, so that it can continue putting up memories without somehow becoming overburdened by them? Neither option seems to be exactly what we want.
I don't know what you mean, but clearly the average length of our lifetime is the result of millions of years of evolution. While it can be stretched a bit with current technology, our bodies and minds are not built to last more than that. As in an old car, all the parts start to fail after some time. (It is not just the telomers getting shorter...) That average lifetime is clearly what natural evolution found to be best for our species (and all mammal species I know of) until we started making fire and bows. Since then, it is not clear where evolution is taking us...
The whole point is that humans will not be the same as before, we will change as a species. It is evolution still, but now technology IS part of human evolution.
You say that the average length of our lives is the results of millions of years of evolution.... which is true, but only to an extent Jorge.. because if you look at figures from 100 years ago, it would seem that millions of years evolution, evolved us to a point where life expectancy was merely 40 ish years old.
Now a mere 100 years later (a nanosecond in traditional evolutionary terms) the average lifespan of a human has doubled, so much for millions of years of evolution.
http://ourworldindata.org/data/population-growth-vital-statistics/life-expectancy/(once upon a time not so long ago, infant mortality was very high, and that was considered natural.. and was also the combination of millions of years of evolution... another statistic that has been turned on its head, in a short period of time , unnatural even you may say)