Hebrews 5:11 Concerning this we have much to say which is hard to explain, since you have become dull in your hearing. 12 For even though by this time you ought to be teaching others, you need someone to teach you over again the first principles of God's Word. You need milk, not solid food. 13 For everyone who continues to feed on milk is obviously inexperienced and unskilled in the doctrine of righteousness, for he is a mere infant!
•14 But solid food is for full-grown Believers for those whose senses and mental faculties have been trained by practice to discriminate and distinguish between what is morally good and noble and what is evil and contrary either to divine or human law.
After reading these passages it is relevant to ask:"What did the author of hebrews think about adult development?"