I personally do not train youth, so I will say that up front. 🙂
But, if this is individual personal training, why would you charge any different based on age? You would still need to assess the youth and movement of his body, see if he has any prior injuries, surgeries, or orthopedic issues that need to be taken into consideration, plus design a program based on his own individual needs.
Again, I do not train youth, but I would not underestimate your value to that population and discount just based on age.
Hope this helps, and best to you and good luck.