I stand my ground. Children have the most neuroplastic brains capable of learning multiple languages simultaneously and having them become instinctive.
Adults are largely screwed on that front.
Most masters of various practices started when they were children and people that got into the practices later on often can never come close to the same level.
Age 18-23 or whatever where people say they are the sharpest is just like the point where you know the most before neuroplasticity starts degrading faster.
https://pediatrics.aappublications.org/content/28/5/764
This somewhat suggests that the episodic physiologic consequences of diabetics are linked with iq differences, which makes sense considering hypoglycemia and acidosis are direct hindrances to metabolic output and integrity.
Why would running make you smarter? It is known it does 100%. Well running improves the efficiency of mitochondria and at a larger scale the blood flow to the brain. But of course that won't endlessly improve your intelligence. It'll hit a cap at your systems maximal efficient output. Similar to genetic muscular strength.
Energy consumption and heat production are directly related to metabolism.