Otis is over a year old and STILL growls at me if I don't play with him when he wants

!! I make it worse because it is SO funny - he will drop his toy and wag his tail as he does his little growl. I try not to encourage him to do that.... but I have not stopped him from doing that. Sigh.... I guess it is time for me to cure him of that habit before it is too late !! Good luck to ya !