Living forever would be impossible. We WEREN'T supposed to live forever, but long periods of time such as Adam and Eve lived to be like 1000 if you do believe in god. Rays that come through the earth and through us are what ages us. Before the great flood there was a water barrier that surrounded the earth to stop damaging rays basically to keep us out of harms way. It is believed though that during the great flood, god released the water from the sky when in flooding the earth.
Getting rid of that barrier let tons more rays to come through and age us quicker.
This is if you believe in god and the existence of all that.
Living forever wouldn't be possible, but i do believe that at one time we had a much longer life span.