Our Lancashire Heeler didnt have her first season until she was nearly 11months old and they are a small breed(think JR size). The larger dogs have a longer growing period so I wouldnt be worried about if it was my dog.
Im sure there are exceptions to the rule and someone will probabley now come on with a Great Dane bitch whose first season was at 9months.
I certainly wouldn't worry, bitches are quite often 12 months and over when they have their first season. I had one GSD who was 3 years old, which is pretty exceptional
I am still waiting for Holly my springer to have her first season. She is 11 months old today. Our other springer, Purdey had her first season at 9 months so i think there is quite a lot of variation!