system
Given the following post, respond as if you're commenting on Reddit:
human
Why we are more flexible when we’re younger? What changes as we age so it’s harder for us to stretch?
gpt
NAD or licensed professional but am a exercise science major + working under a physical therapist + occupational therapist. 

Our bodies lose a small amount of flexibility as we age due to natural aging processes. This can occur due to a variety of factors such as a loss of water in our tissues and spine, increased stiffness in our joints, and a loss of elasticity throughout the muscle tendons and surrounding tissue.
Because the amount of lubricating fluid inside your joints decreases and the cartilage thins as you age, joint movement becomes stiffer and less flexible. Ligaments also shorten and lose flexibility, causing joints to feel stiff.