thank you for your query
It is very difficult to predict height this way. Though it is likely that he will inherit from his parents, it can be from mother or father or grandparents. So it is difficult to say. But yes it is important that you don't add to his peer pressure of reaching a particular height. His height even at this stage is fine. But yes, some aerobics
and stretching will help him a bit. Give him proper nutrition, protein rich diet and he should do well. Don't worry he'll get good height and whatever height he gets will be great.
Hope that helps
God bless you