Most believe they are full grown around 18 months.
A GSD Dog is fully grown at about 2 and a half to Three yeras of age. A Bitch is fully grown at around the age of 2-2 and a half. They are also suppose to be fully mature by then!!
Our breeder told us that our Black German Shepherd doesn't stop growing until about two to three years! We have a five month old male that is already looking like a full grown dog!