This 2014 primate study found:

“The average magnitude of functional connections measured between neurons was lower overall in the prefrontal cortex of peripubertal [age when puberty starts] monkeys compared with adults. The difference resulted because negative functional connections (indicative of inhibitory interactions) were stronger and more prevalent in peripubertal compared with adult monkeys.”

The researchers found more inhibitory functional connections at the onset of puberty than during adulthood. This repressive functionality presumably develops at puberty because that’s when it’s relatively more needed:

“The bias toward increased inhibitory connectivity we report here for young monkeys might also be an intrinsic feature of human prefrontal cortex at a comparable stage of development.”

One hypothesis of Dr. Arthur Janov’s Primal Therapy is that repression is an important function that the prefrontal cortex evolved.

http://www.pnas.org/content/111/10/3853.full “Age-dependent changes in prefrontal intrinsic connectivity”