The category of T-score between -1 and -2.5 standard deviations that defines osteopenia or low bone mass encompasses about 50% of the population. On average, the general population has T-score that is less than -1 standard deviation.
By age 50, about 35% of women and 20% of men are in this range of bone density. With age, the larger numbers of both women and men have low bone density.
Keep in mind that osteopenia or low bone density is not a disease. You need to evaluate your overall health and risk factors for fracture along with your bone density level to find out if your bone density is a concern that would benefit from treatment.