You can ask your vet doctor about the estimated age of your pet. Feel free to select a birth date that is closest to the vet doctor's estimation, we would recommend you to round up or choose the upper limit if this is vague or the estimation is based on a range.
Your pet's age on the policy decides which rules apply, so it helps to be as close as you can:
If your pet's estimated age is close to 6 or 10 years, ask your vet for their best estimate in writing, so the age on your policy matches your pet's vet records.
Read more: Age limits for older cats and dogs.