Schnauzer, Giant Question

That is a big puppy, my Giant Schnauzer is 14 months and barely 70. My vet and trainer told me that at that age to let the dog determine if it is ready....I was told that at that age she would slow down some about half way throuhg, so when you start seeing that head back, each dog will be different. Mine could walk that long physically but got too hot so we had to go shorter for awhile. Good Luck!