Contradiction with Numbers 8:24
Numbers 8:24 states that Levites could start their service at the age of 25, which contradicts Numbers 4:30, where the age is stated as 30.
Numbers 8:24: This [is it] that [belongeth] unto the Levites: from twenty and five years old and upward they shall go in to wait upon the service of the tabernacle of the congregation: [to...: Heb. to war the warfare of, etc]
Contradiction with Numbers 4:3
Like Numbers 4:30, it mentions serving from the age of 30, but Numbers 8:24 says the age is 25, creating an age contradiction.
Numbers 4:3: From thirty years old and upward even until fifty years old, all that enter into the host, to do the work in the tabernacle of the congregation.
Contradiction with 1 Chronicles 23:24
This verse indicates that Levites were assigned to service at the age of 20, contradicting the age of 30 given in Numbers 4:30.
1 Chronicles 23:24: These [were] the sons of Levi after the house of their fathers; [even] the chief of the fathers, as they were counted by number of names by their polls, that did the work for the service of the house of the LORD, from the age of twenty years and upward.