I once read that the natural life span of humans is 900 years. To make sense of this I have to delve a little bit into my beliefs. First off, I do believe in reincarnation. But beyond this, in the same book that I read about the natural human life span it also detailed a blueprint for our existence here on Earth. I'll try and keep it simple and say that we're here to evolve and that a certain time frame is set aside for this purpose. 900 years is not this time frame just that 900 years is an optimum amount of time to spend in an incarnation.
Some days, like today, I can see how nice it would be to slow bake life rather than charbroil it. Life revolves in cycles. I've identified a general one for myself -- and I presume for others -- of experiencing, followed by processing of the experiences. Almost like a heartbeat if you think about: out as in experience, and in as in process. But I digress. It's a nice feeling when you have enough of a certain kind of experience that you can learn from them. Sometimes you only need of 1 instance of the experience, sometimes many more, either way the learning comes at some point. I think this why 900 years might be a better life span than say the current of a general max of 100 years.
Something I realized as a teenager is that people biologically grow older but psychologically they can stay quite young. Quantity of time isn't necessarily the goal, it's how you spend whatever time you do have. Life's all about choices.
One choice I've made is that I want to live in a world of peace and love. I'm tired of strife. I'm tired of wars, tired of killings, tired of abuse. We treat each other so coldly so often. I've been around a few spiritual forums over the years and something I've seen a lot of is that people wouldn't want to live 900 years even if they could. But see, it's still a choice. Our world doesn't have to be this way. It would be nice to start over though. We wouldn't have to make the same choices that we so often have throughout human history. We could be nice to each other.
Something else that was interesting in the book was that physical aging of the body isn't the design. Were you to live 900 years instead of physically looking older you'd just get tired with life and die. How different the world would be if we experienced that. No longings of youth because, let's face it, people only want the physical appearance of youth and not the relatively naive mental state. A super long life span would probably eliminate the intermingling of relationships and ownership. The ideal of marriage, i.e. spending the rest of your life with one person, would just be unthinkable! Could you imagine spending hundreds of years stuck to the same person. :)