Calorie restriction has shown anti-aging benefits as well, does metformin mimic this by restricting glucose/calorie absorption? Does this mean you can have your cake and eat it too?
Intermittent fasting has been shown in a few cases to exceed the benefit of caloric restriction (and it's generally easier to follow: http://www.pnas.org/content/100/10/6216
I mention that because the cytological benefits of IF are also accompanied by well improved glucose regulation metrics. There's a good chance that those changes are at least partial drivers for the overall benefits.