For AMF it's a lot easier to estimate the effect than it is for anti-aging research. GiveWell purposefully started with a focus on interventions for which the can study the effect.

GiveWell writes:

Medical research : As of November 2011, we are just beginning to consider the cause of medical research. Conceptually, we find this cause promising because it is possible that a relatively small amount spent on research and development could result in new disease-fighting technology that could be used to save and improve many lives throughout the world. However, we do not yet have a good sense of whether this cause has a strong track record of turning charitable dollars into lives saved and improved.

You find a bit of data gathering under http://www.givewell.org/node/1339

More recently GiveWell Labs which then was renamed into the Open Philanthropy project will put more emphasis in that direction.

Articles that were written are:

http://blog.givewell.org/2013/12/26/scientific-research-funding/

Why explore scientific research? We expect it to be a difficult and long-term project to gain competence in scientific research funding.

http://blog.givewell.org/2014/01/07/exploring-life-sciences-funding/

“What are the best opportunities for funders aiming to contribute to progress in life sciences (i.e., biology and medicine)?” This post lays out what we’ve done to date and how we plan to move forward.

http://blog.givewell.org/2014/01/15/returns-to-life-sciences-funding/

“What are the best opportunities for funders aiming to contribute to progress in life sciences (i.e., biology and medicine)?” This post lays out what we’ve done to date and how we plan to move forward.

GiveWell Labs managed get Steve Goodman and John Ioannidis matchmaked with the Laura and John Arnold Foundation at the tune of $6 million.

Meta-Research doesn't sound as sexy as anti-aging research but if we want to have good anti-aging research we need a good basis in biology as a whole.

Anti-aging research is a catch-phrase and it makes sense that it's decently funded but alone it won't work. Biology as a whole needs to progress and chasing after shiny anti-aging targets might not always be the most effective use of money. Do you have a reason why you think it makes more sense to speak about anti-aging research than it makes sense to speak about life-science research?

Buying a 50-second increase in life expectancy for a megabuck seems very doable.

Please do a Fermi estimation of how you arrive at that conclusion.