According to the record, due to their unbelief and murmuring, only the young survived to go into the promised land, the rest all dying in the wilderness and particularly, Kadesh Barnea. Moses, in fact, climbed the mountain on which he expired and died, a healthy man, at the age of 120. Many were likely aged but healthy when they exited Egypt. They would have died off in the wilderness or at Kadesh.
I think you're missing the point. They were in the desert for 40 years. The average lifespan was 40 years. That means nearly every one who started the journey should have died in the desert.
So you're saying that even though the lifespan was 40 years in that time frame, this did not apply to those in the desert?