I didn't know anyone claimed longevity as a benefit of a low-calorie diet. I'd always heard "low-calorie" used to combat obesity. And less obesity == more longevity. But never "love longer on fewer calories." Whether this is scientific demonstrable is another matter entirely.
My personal theory is that avoiding gluttonous behavior will do you just fine. Stop when you're full. If you can do that, then you probably have the sensibilities to eat a well-rounded variety of foods. And you're done. That's it. Self-control & variety, Live Forever®
If it were really that simple, we'd have no fat people (me included). Compulsions are a hard thing to control, and if you add it to the fact that a lot of addicting substances are the basis of everyone's diets (sugar, salt, loads of carbs), then you see a compounding issue: personal/psychological issues + chemical stimulation from the food you eat = hopeless obesity...
A bunch of famous studies on mice found that caloric restriction added years to life. It was related to the oxidant/anti-oxident craze of the past decade or two.
My personal theory is that avoiding gluttonous behavior will do you just fine. Stop when you're full. If you can do that, then you probably have the sensibilities to eat a well-rounded variety of foods. And you're done. That's it. Self-control & variety, Live Forever®