My daughter is now 17 months old and only has her 2 bottom teeth and 4 top teeth. She started having "teething" symptoms when she was like 6 months old, but the first teeth didn't come in until 10 months (bottoms, both at the same time) Then she got her 2 latteral incisors (not the 2 very front teeth, but the 2 on the sides) so she looked like a vampire for a month or so before the 2 fronts came in. I feel like she has been cutting all of the rest of the teeth since her first birthday. Gums are swollen and white, feels hard in her mouth, but NO MORE TEETH have come in. I used to be a dental assistand before I had her, so I am pretty much preprogramed not to worry too much. I think all kids grow at their own pace. A neighbor of ours has a little girl 2 days younger than my daughter, and she has ALL of her teeth already. I guess we should just wait to see. I think if your son had NO teeth at all by 18 months then you need to be concerned, but it sounds like he is growing faster than my daughter anyway!