The evidence for metformin to slightly slow aging is not robust. It's nowhere near as good as that for rapamycin, for example. Aspirin and ibuprofen have arguably similar results in short-lived species. Which is a good argument against getting interested or excited by those results. As a general rule things that extend life by 30% in mice, worms, flies, etc, have negligible results on human life span; these short-lived species have highly plastic life spans, and we do not in comparison. Messing around with drugs in this very simplistic way is not the path to rejuvenation and radical life extension. The best data is for calorie restriction and growth hormone receptor loss of function mutations, since we have human populations for both of those, and I can tell you that they aren't living much longer than the rest of us.

For the all over the map and not all that impressive nature of metformin data, take a look at the table in this open access paper:

http://impactaging.com/papers/v4/n5/full/100455.html

The reason why metformin is getting attention now is because a coalition of researchers are using it as the narrow end of the wedge to change the FDA position on treatment of aging, which is currently that aging is not a medical condition and thus no-one is permitted to treat it. They cannot possibly expect meaningful results on aging, but that's not the point; the point is to run a trial with something that the FDA cannot object to on other grounds because it has been used for decades and is already approved for other uses. Thus the FDA accepts a trial to slow aging, and the door is open to all the methods that might actually have some meaningful effect in the future.

http://news.sciencemag.org/biology/2015/09/feature-man-who-w...