Bone formation starts in the fetus 6 months before birth and is not generally complete until adolescence (between ages 13 and 18). Bone formation is never really complete. Bone is a living tissue made up of protein, calcium and other minerals, and water.

How old are you when your bones harden?

Most people will reach their peak bone mass between the ages of 25 and 30.

At what age does bone degeneration start?

Bone and joint degeneration can start in middle age, but it is most common in people older than 65. Other risk factors include: Chronic stress on your joints from activities such as sports and some jobs. Family history of osteoarthritis.