"It is theorized by some that when it is discovered exactly what allows some cells to be biologically immortal that it will be possible to genetically alter other cells to have the same capability (most believe telomere length is involved). It is further theorized that it will eventually be possible to genetically engineer all cells in the human body to have this capability by employing gene therapy and thereby stop or reverse ageing, effectively making the entire organism biologically immortal."
http://www.answers.com/main/ntquery;jsessionid=1ox06c3cxhyvf?method=4&dsid=2222&dekey=Biological+immortality&gwp=8&curtab=2222_1&sbid=lc01a&linktext=Biological%20immortality

Would you desire your lifespan to be 120 years, 150 1000 etc..? At what point would you call it quits?

I am not sure. Depending upon whether or not my physical and mental acuity remain (or becomes wink ) sharp, my decision resides. Is the Earth habitable..is the future certain and stable..?

Sincerely,

"My God, it's full of stars!" -2010