The average weight of an thirteen year old girl is 101lbs. but that is based on the average height of an thirteen year old girl. If you are taller than an average thirteen year old girl you will weigh more.
The average weight of a one month old baby is anywhere between 6.6 to 11.2 lbs. However, it is known that some newborns will slowly lose weight after the one month mark then gradually put the weight back on.
At 3 months, the "typical" baby weighs 13 pounds and measures 24 inches. But don't worry if your baby is smaller or larger. Babies, like adults, vary in size and shape. In fact, the "average" weight for a 3-month-old can range from 9 to 16 pounds and the "average" length from 22 to 25 inches.