Male puberty can start as early as 11 years old through 17 years old. most common is generally age 14 or so. I don't know how close to age 16 he is, this generally occurs when there is an increase of the hormone testosterone.
Here is one site that breaks down some of the common changes and at what age. However keep in mind this is just a guideline and can vary greatly from one person to the next.
read here
If he has nothing pointing toward puberty, I would have him seen and have a full blood work up, including check his hormone levels, thyroid, and all glandular functions as well. This will give you a better clue as to what is exactly going on.
Best of luck, Hope this helps, If you need anything else please feel free to ask. If you found this helpful don’t forget to click the *Accept* button.