Because 1% of 90 years = 9 months in the womb, then
1% of 900 years = 90 years in the womb.
Is this what you are saying?
No, he's saying that if the original speed of the postulated decrease in lifespans had continued at the same rate, we wouldn't even be living nine months beyond conception at present day.
No, because a drop from a 900 year lifespan to 150 in five generations, extrapolated to 300 generations, would leave little lifespan left.