My large breed often do not have a season until 14 - 18 months and then cycle pretty regularly. Vino was 18 months 1st season then 6 months then as I wanted to breed her she went 8 months, but she carried a litter fine and is now back in season 5 months after pups were born. Aileen
We had one who had her first season at 14 months and went on to have seasons every 7 months. Another girl again first at 14 months only comes in every 13 months. (Same breed).
One of our bitches had her first at 13 months....every season after has been every 6 months almost to the day. She has had a litter of nine and now back to her usual 6 monthly cycle.