I had a Maine Coon mix that grew to be 22 lbs. His spine was level with my knee, and he was not even chubby, just large and big boned. His head was so big that I could lay my hand on the top of it and my middle finger would not quite reach his nose. His paw would cover my palm. Fortunately he was the sweetest, best natured kitty I have ever had. His name was Leo, a red tabby, and he has gone to the Bridge.
It took him about 2 years to reach is full height, a little longer to fill out.