Intellectually juvenile

[Zipporah Schumaker]

The term intellectually juvenile politely describes someone who is unintelligent, [unwise] or just not the sharpest knife in the drawer.
The term intellectually juvenile applies to a person, or group of people, who are not as developed in their thinking as they should be for their age, education, experience, [geographical] location, social environment, etc.
Background: Most of the people who are constantly calling other people stupid are well known to be not-so-bright-themselves, and thus the word stupid has lost its credibility and power as a descriptive term. The word stupid is overused, [low brow] and passé.