What's an average resting heart rate for a 15 year old boy?

Probably 50-70: Depends on how much exercise /physical activity he gets. But a true resting hr for the average adolescent male probably runs 50-70. For those who do sports, it can be lower, into the 40's. I grew up playing competitive sports, and at that age through my early 20's mine was about 40-42. If its considerably faster, say 90 or greater, i would seen by a pediatric cardiologist.