"The first person to live to [200, 300, 500, 1000] has already been born"

[Amine]

Why would we think that? Why wouldn't we think the opposite, or neither? Are we to believe that knowing they will die makes people more productive to make the most of their time? One could just as easily make the argument that it makes them apathetic to make changes in the world they will never get to benefit from.

Take a look at science, just as one example.  It's rare to find the proponents of a theory among the camp of those who later overturn it with a new theory.  Old eyes breed old answers.  Somebody new comes along and takes the establishment, kicking and screaming, to a place closer approximating the truth.  I don't know whether or not someone believes (or wants you to believe) that mortality makes us more productive, I don't think so, in any case.   

Who said there wouldn't be new people? Also, theoretically if we had the technology to cure aging we would probably also understand the neurophysical basis of the sort of openmindedness young people have. We've barely begun to tap into that sort of thing. There are *certain* sources of creativity out there that happen to be highly illegal to even research most of the time. It's at least a starting point. Problems tend to have solutions.

What is the alternative? You would rather let people die of old age when they have the cure to ageing or overpopulate the planet so that them or others starve just so they can make some babies who would have to go under that exact same process?

When you talk about those things, think about the context you're talking about them in.

Yes, I would rather just let it be as nature intended. Die of old age and make room for new life.

Okay let's ignore the fallacy and run with that. What's the right age? You don't seem to be denying that the technology might be possible, so let's assume it is. You get to look and feel and physically be as young as a 25 year old indefinitely. How old will you be when you decide to commit suicide? Or will you simply go the Amish route and refrain from taking a medicine that will keep you healthy and young and let yourself age naturally? If that's the case, are you already the sort of person who refrains from taking health measures?