How do you define such a thing?
If it is done on tables of people who have actually died, then probably about 15 years.
Ray Kurzweil said last month that the diligent have already reached longevity escape velocity (adding more that a year to their life expectancy for every year that they age – ie indefinite life extension).
Most people are not diligent, so most probably wont make it at this point. But that will change as technology improves and the less diligent can enjoy the benefits.