Well, here are three teenage boys (15 yrs). Not really much help -- just a chance to show off the kids. Taken this year. These guys are all over the map -- very different from each other. Someone would have some trouble on their hands making the mistake of thinking one size fits all! Something to remember when dealing with a set of two or more closely aged teenagers/pre-teens siblings.
Scanned 11x14 contact print. Taken with a 270mm lens -- exposure was about a second, maybe two, using the lens cap, so the boys' heads are not sharp, but sharp enough!