At 16 it is unlikely he is at his physical peak. Some genotypes mature earlier than others. If he doesn't have a full beard, squat 400+ and bench around 300 then he has a ways to go. No amount of lifting before his body is ready is going to achieve much. Besides physical maturation, mechanics are usually where the bug chunks of velo can be found. I just checked my sons stats for that age. He was 6 feet tall and threw 82 at his first PG event. At 21 he is over 6'3'' and has touched 95; and just yesterday he said he had figured something else out with his mechanics.