I recalled that wrong, it was more linked to the occurence of cellular disease as opposed to ageing, in turn effecting life expectancy.
With higher IGF levels the body is in constant growth mode, new cells, rapid expansion and more chance for things to go wrong at the cellular level etc.
With lower IGF levels the body "switches" to maintenance and repair.
This was all taken from a documentary, while although the science was there, was adapted for viewing purposes.