Some friendly advice please!

Our precious little Landon is going to be three yrs. old in three months from today. He is still not talking! No sentences yet at all! We have had him evaluated from DDI advantage, He passed everything he has also been seen from his pediatrician, and we were told that he is fine, His Pediatrician did however say that there would surely be nothing wrong with getting him into some therapy but we yet have not. He was a late walker, but something inside as his Mommy tells me there is more to this.........Could I be right?? Or is it just the worry wart mother worrying too much again?..... I AM WORRIED!... Should I be?... Or should I not be? I will take any advice you are all willing to give! Should we give it till he's three? Or should we go ahead and get him into speech therapy now? The words he can say are....Mommy, Daddy, No, Ya, YAY, Moon, Ooooohhh!!!! (meaning something stinks! LOL!) He says Two, .......There are a few more, I just can't think right now! He does understand everything that we say, and he will go get anything we ask him too......He's very smart! Just not talking.....NOT AT ALL! I don't know, I think I am more confused than anything! ADVICE PLEASE!!!!!!! All the Grandparents says he's fine, just not ready to talk yet, or like my Dad says..."maybe he has nothing to say!" Trust me-------if he could talk, he would have PLENTY TO SAY!!!!! :) Oh and his Daddy doesn't seem to worried either, but I think his Daddy does all the talking for him also! TOO MUCH BABY TALK JOHN!!!!! LOL! :) I LOVE THIS LITTLE BOY MORE THAN I COULD EVER EVEN EXPLAIN!!!!!