Is 104 pounds a healthy weight for 16 year old girl? i exercise four times a week and try to watch what i'm eating.

Depends on height: Healthy weight depends more on height than age. If you are 5 ft 0 in to 5 ft 2 inches then 104 is a healthy weight. If you are under 5 ft it might be a bit high, if you are 5 ft 3 or more you might be underweight. See http://www.Rush.Edu/rumc/page-1108048103230.Html for more information being underweight can be as serious as being overweight-many teen girls have an unhealthy obsession with weight.