Honestly, I would hold off a bit too. It sounds like he's on track (or ahead) in everything else. The fact that he understands and makes noises, etc are really good signs. Have you considered signing with him? It was really helpful for us and does not delay speech development.
If your Dr is not concerned, I wouldn't be. They've seen it all and usually have a good idea of the range (and it is a range) of what behavior is considered normal at this age. It sounds like he understand and that is the hardest part. Talking will most likely come. I waited until about 27 months before having my son evaluated and that was still considered fairly young. Many prefer to wait until about 2 1/2 since that is pretty typical for a lot of speech to come in. And wouldn't you know it. He started really talking at 2 1/2!