To borrow from Tyler Cowen.
Skeletal maturity is one example of continued growth into the adult years. Although most epiphyseal growth is completed in late adolescence (16 to 18 years), the long bones may continue to grow until approximately age 35, and the vertebral column until about age 30. This continued growth in the long bones may add up to one-fourth inch to an individual’s height. In addition, certain areas of the braincase do not reach maturity until well into adulthood. This continued growth is evident when men (and women) who wear hats notice that they have to purchase larger sizes as they age. [Emphasis added]
This is from Lifelong Motor Development (4e, 2004) by Carl Gabbard of Texas A&M.