What stops the skull/brain and jaw from growing in childhood years ? im insecure about my small head circumference im 6'2 tall

Genetics: Head size in general is determined by genetics, with 90% or more accomplished by age 9. Some medical conditions can increase or decrease head growth, but these lead to obvious changes in intellectual performance. There is a wide range of normal adult head size and your doc could review your concerns and investigate other issues if needed.