Are speech impediments hereditary? 13 month old doesnt 'say' anything?

My now 17 month old son didn't start walking until 15 months and at his 12 month check up could say only "mama". He is now running and saying several words most of which are understandable. I think your son sounds perfect and is just developing in his own time. My oldest son now 3 1/2, could only say three words at the age of 2 and I was positive he was autistic. He has been in speech therapy for a little over a year and is doing wonderful now with a vocabulary in the four to five year old range and, despite my worries, is not autistic ;). If your are concerned then setting up an early meeting with your pediatrician isn't going to hurt a bit. Not only will it put your mind at ease, it will help diagnose any problems if they are there. He sounds completely normal to me but you are his parent and should do what makes you comfortable.