Deuteronomy 2:15 (ESV)

15 For indeed the hand of the LORD was against them, to destroy them from the camp, until they had perished.

The wilderness generation did not die out form old age. Rather, Moses speaks of the dying out of the wilderness generation as a result of the Lord's warlike action against them. This is a massive reversal for the people who had previously experienced great blessings from the Lord. But their stubbornness and rebellion prevented them from seeing the land