The "ancient rule of thumb" was really made by health insurance companies so that they wouldn’t have to pay out claims for people who are "obese". They set their standards impossibly low so that a very small percentage of the population would be considered a "healthy" weight.

You also need to take into account your bone structure…are you fine boned, medium boned or "huge boned"? Here’s a way you can tell: Wrap your left hand, from middle finger to thumb, around your right wrist (if you’re left handed, wrap your right hand around your left wrist) right where the wrist bone is. If your thumb and middle finger overlap, you are fine boned, and could stand to lose a small weight. If they just touch, then you are medium boned and you are probably at about the right weight. If there is a gap, then you are huge boned and you’re weight is fine, and you could even stand to gain a few pounds.

Please remember that at 13 you are still growing and your body needs excellent nutrition. If you try to diet at your age, and you do something crazy like try to lose 40 pounds in 3 months, you may cause health problems that won’t manifest themselves until you are much older.

What you really need to do is work out and tone up your muscles. If your parents belong to a health club, question them if you can go, too. Yoga and Pilates are fantastic classes that are offered at most health clubs. They tone and strenghten your muscles and help increase flexibility. If your parents don’t belong to a health club, question them to buy you a Yoga and/or Pilates DVD to do at home.

To get you started, I’ve pasted a link to one of my favorite workouts called the Skinny Jeans Workout. I don’t have a step thingy, so I just use the stairs in my house.

Trust me, when you are my age you’re going to look back at your junior high pictures and go "What the heck was I thinking??? I looked fantastic!"