Yes i know what you mean, i think commonly most of mine come into first season at between 9 -11 months, however poppy did not have her first until she was 13 months I was beginning to wonder if I had missed something
but she went on to have a perfectly normal season
See the thing is ... you are missing a trick here, the best and foolproof way to ensure your girl comes into season is book into an important event, Eg, enter into a show you dont want to miss, book into a training workshop or the best one is of course book into a holiday that you plan to take the dogs on and voila along comes " the season"
to coincide with important event