These days, I’ve been attending classes with high school students and suddenly realized that high school might really be the peak of many people's intelligence.

The core difference isn’t in brainpower, but in attention. After leaving the student identity behind, the adult world is filled with trivial worries that drain emotions and effective cognitive resources.
Of course, compared to teenagers, we have an absolute advantage — in cognitive breadth and critical thinking ability. During class, you can clearly see the surpassing, but focus drops off dramatically.
That’s why I now understand why many experts emphasize the importance of meditation. Actively clearing memory can regain control of attention and help the brain skillfully return to a focused state.