Biologically, it's not as simple as maintaining good health and reducing life's stresses. There's both a built in limiting factor, both genetically speaking and cells run out of telomere length at the ends of their chromosomes; thus, the cell simply stops dividing. Aging is even more involved than that. It's not a simple matter.
However, there are other means for extending the natural useful human life span.
1. Genetic engineering
2. Embryonic stem cells for rebuilding tissues and organs
3. Human cloning
4. Uploading / downloading consciousness
5. Engineering artificial brains and organ systems, I kid you not.
6. There's still yet other ways to approach the problem
If we really wanted to extend human life, we have the technology to accomplish it today.
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See: Teen baby narrows search for 'master ageing gene'
http://www.newscientist.com/article/mg20327154.700-teen-baby-narrows-search-for-master-ageing-gene.html
Stem Cell BREAKTHROUGH
http://www.pbs.org/wgbh/nova/sciencenow/0305/03.html
Scientific and Medical ASPECTS of HUMAN REPRODUCTIVE CLONING
http://www.nap.edu/openbook.php?isbn=0309076374
Artificial Life
http://www.pbs.org/wgbh/nova/sciencenow/3214/01.html
World's first brain prosthesis revealed
http://www.newscientist.com/article/dn3488