DS was 15.5 months.. I didn't think he would ever let go of the couch!!!! His cousin (who is 2 months younger) was walking way before him and I felt like he was really slow and that he would never catch up..
But now he is walking..... so it will eventually happen.. try not to stress too much about it.. just think.. he's working on his brain development instead - so he'll be more intelligent... lol