Thanks to all for the info! FWIW, he drinks a Muscle Milk shake now after every time he lifts/trains. He also drinks a ton of milk, period. It seems like we're buying milk every other day because we're running out of it because of him. He also gets a lot of sleep. And, he's not a junk food kid. (My wife is a bit of a foodie, been vegan for a long time, and we really don't have junk food in the house.) I would bet that my son's body fat is around 8%. He's got an 8 pack and is very defined. He's always been that way. (Sometimes I tease my wife that I want a DNA test because I was never that way. But, I grew up in a house and in a time where we ate donuts or pop tarts for breakfast.)