There is all kinds of information on Creatine in the strength and condition forum. Go to that section and do a search on it and make up your own mind. I personally think teenagers should focus on good eating habits, lots of rest (overlooked), a good work out program with some additional protein supplements after workouts….. also lot’s of H2O (overlooked)
Sounds like he is doing the right things, remember there are no magic bullets, and it is difficult to access X mph per year, there are just too many variable - just lots of hard work required. Mine went from low to mid 70’s to low 80’s Fr to Soph. so it is possible, but it will probably depend when he hits puberty and the subsequent body mass growth. Good Luck!