Hebrews 5:14

14 But solid food is for the mature, who by constant use have trained themselves to distinguish good from evil.

Read Hebrews 5:14 Using Other Translations

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.
But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil.
Solid food is for those who are mature, who through training have the skill to recognize the difference between right and wrong.