Charles Ellicott Commentary Numbers 14:29

"your dead bodies shall fall in this wilderness; and all that were numbered of you, according to your whole number, from twenty years old and upward, that have murmured against me," — Numbers 14:29 (ASV)

From twenty years old and upward.— Rashi thinks that these words were used to show that the Levites who were numbered from a month old and upwards were not included in the general sentence of destruction, and that, consequently, it is not surprising that some of them, as, e.g., Eleazar, entered the land of Canaan.