Well, he is a bit big for his age (speaking about the standard) but, he does not look like he is carrying too much excess weight. At 9 months you are past the critical period as the joints and epiphyseal plates are more calcified and less vulnerable. The first 6 months being the most "dangerous" so to speak. I would continue to keep him lean, he will be what he is, large. Keeping him lean and active is the key, which it looks like you have a good start doing.