I wouldn't worry. I have a late talker as well. She just turned 2 and has doubled her vocabulary almost overnight recently. She walked at 8 months but didn't start saying things til around your son's age...even now her vocab is very limited...but she can understand everything!
Momma, daddy,juicy,no,why,nite-nite,bye-bye, auntie,matthew, cereal,what, brother....this is her basic vocab right this minute. The doc isn't worried, she is the baby and hasn't had to talk....might be the same with your son....is he the first? When they no you get them whatever they want there really isn't any incentive for them to be more verbal.
Hope this helps!