Better chance of finding good info when you google it. Imo if you arent fat i woudnt care about your weight. If you have to much fat on your body, you can probably tell you are a bit to heavy and or out of shape by just lookig at the mirror.
I really think the mirror should be your go to source. On a age like 13 it is really hard to say. Because some have hit puberty already and others not so much. Some have been growing alot alrdy and will not grow that much anymore others still have to hit their growing point. All these things play a big factor. Just take it from the mirror and every person will know if they could lose a few extra :-)