If technological progress continues exponentially (including increases in human or machine intelligence to make them possible) then our understanding of biology and life-extension will continue to increase, and many such life prolonging-treatments will be made available to the public.

If one life extension makes you live 5 years longer, and during that time an new one comes out that lengthens your life by a few more years, you can see how one might keep "catching" these just in time and thus gradually transition from mortal to immortal.