Question 1 is rather speculative. First of all you need to believe in the Old Testament to buy into the ages given. However, there will not be a second of all because if you do believe in it no scientific proof will ever matter to you (except if it can prove that there has ever been people who became almost a thousand years old). In JRR Tolkien's books elves can live forever.
Here's a gift for you - I think you'll love this web site:
The Biblical Ages of the Patriarchs
I suggest you try out all the creationist issues with that site first.
Question 2 and 3 are easier to answer:
2) People already live to be 120. You can even find lists of people on the web. As for what the future brings...
here is a rather technical speech on the future of aging
3) Aging is not specific to people - it is something we see in every living being. People age differently because they react to the environment in which they live, and the genes they are born with. Here's a good link on aging:
Why Are We Allowed to Age?