E.B.
Without knowing your son, I would say - if he wants to take guitar lessons, sign him up for guitar lessons! I do agree that piano lessons may be just as beneficial, but if he isn't "into" piano, he wont stick with it. Music lessons of any type have to teach basics of theory, so he will learn those basics that you are wanting him to learn. I know for my 15 year old, guitar is sometimes his sanity. He started lessons at 9 and now he can play just about any instrument he picks up. Get him started now, he will need something he can hang on to at times! (so will you!)