Thats a hard question to answer… we really don’t have a good translational model for going from other model organisms (e.g. mice, etc.) to humans, in terms of longevity drugs. Rapamycin was really the first (and best) drug to do this in any significant way.
and while the above poll doesn’t address the dosing issue, the benefit predicted by these longevity researchers and doctors overall, suggest somewhere between 5 years and 10+ years benefit.