There is no set answer for the average weight of a 5' 26-year-old, because body weight is a misleading measure. Since people have different builds, different people of the same height and sex can have the same percentage of body fat and yet have different body weights. Therefore, what is important is body composition. The reason for this is that muscle weighs more than fat. What counts more than your body weight is your percentage of body fat. If you are a male, your percentage of body fat should probably be about 10 to 15% for good health. If you are a female, your percentage of body fat should probably be about 15 to 20% for good health. To determine your percentage of body fat at home, obtain some plastic body fat calipers and do a simple skin-fold test. Body fat calipers are not expensive, are readily available to buy, and can replace a scale or balance.