“all who were numbered of you according to your whole number, from 20 years old and upward who have murmured against me.” This verse says things that differ from what is preserved in the Christian tradition. Numbers 14:29 makes it clear that not all the Israelites except for Joshua and Caleb died in the wilderness, as is often taught.
The people who died in the wilderness are specified by three clauses: all who were numbered; all who were 20 years old and older; and all those who murmured. The Bible is clear that the “whole congregation” murmured (cp. Exod. 15:24; 16:2, 41; 17:3; Num. 14:2). However, there were many people who left Egypt who were not yet 20 years old, and lastly, not every Israelite was numbered in Moses’ census.
It is very clear from reading the Book of Numbers that the Levites were not numbered with the other men (cp. Num. 1:47-54). That explains why God specifically spoke to Aaron and Moses about their dying in the wilderness, and why Moses thought he should be allowed in. Note that it was because God was angry with Moses that he was not allowed into the Promised Land, not because he was older than 20 when Israel left Egypt (Num. 20:12; 27:12-14; Deut. 1:37; 3:23-27).
It is also possible that the women of the generation that left Egypt were allowed into the Promised Land, because the only ones numbered were the men. However, the Bible is silent about that and does not say one way or the other.