How long would effects like this last? I mean, let's say a bunch of children donated blood for the cause, and we used it to replace the blood of a senior citizen. I don't know how to phrase this properly, but how long does the blood maintain the youthful qualities? Do you constantly need new blood coming in from a young donor? Do you receive it once and you're good for a week? A year?
In any case, this will never turn into cross-generation blood transplants on a regular basis. The present system of medical regulation is heavily biased towards demonstrating mechanisms. If you can't explain your mechanism you are not getting approved by the FDA, or at least not until such time as everyone else in the world is already doing it and the bureaucrats are made to look bad - see the last decade of stem cell transplants for the way in which that happens.
So the attempts at therapies that result from this will likely be delivery of proteins or interference with proteins to put a thumb on the scales of metabolic machinery. At which point it lasts for the period of time in which you are getting regular injections.