For women, bone health begins at a young age. A woman acquires about 85 to 90 percent of her bone mass during childhood and adolescence. By age 18, her bones are completely done forming. If there is not enough calcium deposited in her bones during childhood, they may become weak later in life, leading to bone disease such as osteoporosis. Fragile bones easily fracture or break, especially in the hip, spine and wrist.