As a Demography student, I can tell you that, if everyone on the planet were to live as "green" as I do, with the same diet, commuting patterns, housing conditions, and airplane usage patterns, we would already need approximately 4 planets to provide the needed resources.We already have horrible over-population, just thing what kind of a resource burden that would be if everyone was living to be hundreds of years old.
We would be living in a sea of Indians from the northern provinces of India.Especially if the birth rate stayed the same.