What should i weigh for my height and age? i'm 5'4, 18 years old.

Targeted weight: A target weight based only on age/height and body mass index is 125 lb with a common range from 112-140. Body mass index is an idealized number that assumes average muscle mass and bone structure. Much of what should be your best weight will must accept these variables. A range of 107-139 would still be within what is considered a normal weight range.