My guess is that means to achieve longevity (150+ years) is difficult or were deemed difficult and time-consuming in the given circumstances around the time of Ra contact.
I say this because on the one hand Ra says that the transition period is a likely one hundred to several hundred years and yet harvest occurs upon death, yet on the other Ra says that no time should be wasted on life-extending technologies when asked about them by Don because the harvest is near. If the transition period before full 4D was over 100 years, and human life span as is currently well under 100 years, it would seem that life-extending technologies, if quick and easy to develop, would help increase the harvestability by extending lifespans and lessons of the last 3D incarnation of those natives on the border of harvestibility.
In short, a logical (but not necessarily correct) conclusion would be that Ra suggested not to spend time on life-extension because it would be too time-consuming to develop at this point and would detract from the time spent in spiritual evolution in some fashion. Or perhaps there was something else going on, but it's certainly something to consider.
I say this because on the one hand Ra says that the transition period is a likely one hundred to several hundred years and yet harvest occurs upon death, yet on the other Ra says that no time should be wasted on life-extending technologies when asked about them by Don because the harvest is near. If the transition period before full 4D was over 100 years, and human life span as is currently well under 100 years, it would seem that life-extending technologies, if quick and easy to develop, would help increase the harvestability by extending lifespans and lessons of the last 3D incarnation of those natives on the border of harvestibility.
In short, a logical (but not necessarily correct) conclusion would be that Ra suggested not to spend time on life-extension because it would be too time-consuming to develop at this point and would detract from the time spent in spiritual evolution in some fashion. Or perhaps there was something else going on, but it's certainly something to consider.