I think it depends on lines... my oldest came into season for the first time around 8.5 months of age. I have heard that her daughters have come in for the first time as early as 6.5 months. My yellow girl came in for the first time at 15 months of age, her dam came in at 14 months for the first time. I have a female puppy that is young so it will be interesting when she comes in for the first time :)