If you have an age at death, keep in mind that the resulting birthdate (calculated from the age), may be slightly off. First it required the informant to know the exact date of birth and also required them to make the calculation of age correctly. Without knowing the birth date they used to determine the age, there is no way of knowing if the birth date is correct or not.
Always put the qualifier "calculated" in front of these dates of birth. If the person was "older" at the death, the age is a secondary source for the date of birth and should be treated as such.