Hello, is it possible for a human head to grow smaller over time? an odd question i know.

Unlikely: Once a person has reached adulthood the growth of the skull is clearly complete. The sutures have fused. The skull cannot decrease in size. Externally, there may be the appearance of some decrease in head size if there is a change in the skin thickness or changes in the amount of fatty tissue. But the actual head size really doesn't change because of the constraints of the skull.