The human skull never stops growing.

By the time most of us reach age 20 or so, the bones in our body are pretty much done growing. The growth plates that cause us to put on inches in our youth are now hardened bone, and in fact, adults tend to drop an inch or two in height as worn-out cartilage causes our spines to shrink over time. However, there are a few bones that buck this biological trend. Skulls, for example, never fully stop growing, and the bones also shift as we age. A 2008 study from Duke Universitydetermined that as we grow older, the forehead moves forward, while cheek bones tend to move backward. As the skull tilts forward, overlying skin droops and sags.

The skull isn’t the only bone that has a positive correlation with age. Human hips also continue to widen as the decades pass, meaning those extra inches aren’t only due to a loss of youthful metabolism. In 2011, researchers from the University of North Carolina School of Medicine discovered that hips continue to grow well into our 70s, and found that an average 79-year-old’s pelvic width was 1 inch wider than an average 20-year-old’s. So while it’s mostly true that humans stop growing after the age of 20, nature always likes to throw in a few exceptions to the rule.