Bones are living tissue. We are constantly losing and replacing bone tissue. When we’re younger, we replace more bone tissue than we lose. As a result, our bones become denser, larger, and heavier. Our bone mass usually peaks in our 20s. As we get older, the balance between losing and replacing bone begins to shift in the other direction. We begin to lose more bone tissue than we replace. Bone loss usually starts slowly but gets faster as we reach middle age. Women typically begin to experience more rapid bone loss after menopause, which usually begins around ages 45 to 55. Bone loss in men happens more gradually, but by age 65, women and men lose bone mass at about the same rate.