German Shepherd dog

What is an average timeline for a GSD's growth? I'm mainly asking about male showline dogs. It seems that some dogs mature more quickly than others, is this true? Is a two year old dog done growing, or does he still have "filling in" to do? Is there any good way to estimate the size a dog will be as an adult? In horses, they have 90% of their height, typically, by one year of age, and you can look at frame, bone size, etc, to get an idea of how the horse will mature. Just wondering how people evaluate young show dogs...