a) In a way that's economically viable.
That depends very much on how much protein you need and how much people you can treat. It's possible to spend 100 million to genetically engineer yeast to be extremely optimized for producing a certain protein. A big pharma company can spend that much money when the drug is a block buster drug but researchers who just want the protein to run a few experiments can't.
Given how much people spend on drugs that only pretend to reverse aging or treat one small symptom of it, I'm pretty sure a pill that actually does reverse it would be of major interest to billions of people.
In experiments performed on mice, blood transfusions from young mice reversed age-related markers in older mice. The protein involved is identical in humans.
http://mic.com/articles/88851/harvard-scientists-may-have-just-unlocked-the-secret-to-staying-young-forever