Should I be concerned about my 15 Month old nephew's behavior?

My sister had her third child when she was 43 yrs old. I am pretty sure she was on prozac when she got pregnant. She stopped it during her pregnancy but started up again on it after her son was born. What concerned me was she nursed him. But stopped after three months because he was impossible to nurse unlike her other children whom she nursed for a year. I babysit my nephew three days a week.

I myself have four children and also have babysat other children in the past so I have a lot of experience. My nephew is 15 months old and I am seeing signs of abnormal behavior that are raising some red flags in my mind. First of all, he doesn't say a word...just grunts...not mama nor dada..nothing. At about a year he would say a couple of things like "ruff" for what a doggie says or "again" but he has stopped saying them. He seems very smart. Responds to his name always. He smiles and laughs alot and is very active...all pretty normal except he will not hold his own bottle and refuses to drink from a sippy cup.

At first we all thought it was just laziness...but I have been trying to make him hold the bottle himself and he just screams and clenches his hands as if he doesnt get it. When feeding him in his highchair, he shoves all the pieces of food in his mouth. I try to cut them up tiny but still manages to do it. I can't give him a whole little cookie. I try and show him to take a bite of it but he will shove the whole thing in his mouth anyway! He is also a very picky eater.

He is constantly falling and running into things. He doesnt play with many of his toys just wants things he cant have. He is very destructive and strong! His mother says "thats a boy for you". This is her only boy. I have an eleven yr old boy myself. He was boy through and through but never displayed behavior like this! I dont really want to say anything to my sister just yet being that he is still developing and I am not with him all the time. Help? Does anyone think I should be concerned?