* Small breeds: Typically enter their first season between 6-12 months old.
* Medium breeds: Between 12-18 months old.
* Large breeds: Can be as late as 18-24 months.
It's important to note that these are just general guidelines. Some dogs may come into heat earlier or later.
If you have concerns about your dog's first heat cycle, it's always best to consult with your veterinarian.