UK Labradoodle Association

My two sister Labradoodles, Half poodle and half Labrador ,born December 27th 2014,have not shown any signs of a season. Can someone kindly advise me of when this is likely to happen ?
Is it possible that I could have missed this ? I watch for swelling of the vulva,but have seen no difference.I am fairly new to being a dog owner,I have a three year old male yorkshire terrier,( neutered ),but never had to think about this problem before.
Having read many books about the dogs,I have not found any help as to when I can expect this.

I was very confused too when Willow (small standard) hadn't come into season when she was nearing a year old. But a few weeks before a year, her vulva did swell a bit. So I wondered if this was it so was ultra vigilant. But the day before she was a year old she started bleeding. Not too much, but enough to be noticeable. She was also cleaning herself more there too. The bleeding went on for about 3 weeks. Then that was it. As to when a bitch comes season - I believe that the bigger the dog, the later it could be, but every dog is different. Good luck.

Not to worry - Phoebe was 18 months before she had her first season. I was very worried by that time, but the vet said it was unusual but not unheard of. I guess they do things in their own sweet time!