As long as the dr is not worried no need to be worried. My best friend daughter had 4 teeth for the longest and when she turned 2 teeth just started coming in like crazy, bad for the kid bcuz of the pain all at once.
give him a wet rag to chew on and schedule an appt. with a dentist its probably nothing to worry about hes most likely just a late bloomer
I would suggest having your son/daughter take him in for his 18 month check up and teeth is one area they should check. But if they don't then have them bring it up. The longer teeth wait to come through the healthier they actually are, less likely to get cavities and have more calcium. A dentist could take x-rays to check to see that the teeth and developing properly under the gums and ease your mind. Hope this helps! And for now, enjoy his gummy grin :)