Humans don't just shrink with age. They shrink EVERY DAY.
Humans shrink and regain height daily, sometimes as much as 3/4 of an inch in one day. When we move throughout the day, the fluid disks in in our spinal column compress and we shrink. When we rest at night our backbones reabsorb the fluid and our height comes back.
As our bodies degenerate over time, our ability to grow back our height diminishes over time. This contributes to the loss of height that occurs as we age. It's not uncommon to lose two whole inches by the time we hit 60 years old.