Creatine is not a drug and is not known to be harmful in short term or long term use. If used correctly, in most people, a notice increase in strength is noticed. Some forms of creatine have caused diarrhea and cramping in some people. A 15 year old shouldnt worry about using creatine yet. He should focus on learning how to lift properly and eat right geared towards building strength and size. Once he has built a good foundation(at least a couple years of consistant training) then maybe creatine could give him an extra boost. I have been a personal trainer for 10 years by the way. I have been using creatine for many years with no known negative effects. If he were to go behind your back and use it, it would hurt anything but it really isnt nessesary. Hope this helps;)
Creatine can lead to dehydration. So you must increase fluids. I agree about the age thing. L-Glutamine might be a better choice. Still helps build muscle, regulates blood sugar and can be used long term.
Well I stand corrected. New studies show creatine to be ralatively harmless. Dehydration if any is from the muscles taking on more water. I still think that a 15 year old doesn't need it.