Final answer:
Bones in young children are more flexible due to a higher collagen content and lower mineral content, whereas bones in the elderly become denser, more brittle, and less flexible due to increased mineralization and decreased collagen production.
Step-by-step explanation:
The bones of young children are much more flexible than those of the elderly primarily due to higher collagen content and lower mineral content. In young individuals, the bone matrix has a higher proportion of collagen fibers, which imparts flexibility and allows for growth and development. In contrast, as we age, the cellular processes change and our bones accumulate more mineral content, mostly in the form of calcium salts like hydroxyapatite, which can make our bones denser and more brittle. This process is compounded by the fact that collagen production decreases with age, which leads to stiffer connective tissues and joints. The resulting decrease in flexibility and increase in brittleness of bones is why fractures are more common among the elderly.