Hebrews 5 (KJV)

12 For when for the time ye ought to be teachers, ye have need that one teach you again which be the first principles of the oracles (laws) of God; and are become such as have need of milk, and not of strong meat.
13 For every one that useth milk is unskilful in the word of righteousness: for he is a babe.
14 But strong meat belongeth to them that are of full age, even those who by reason of use have their senses exercised to discern both good and evil.