Did It Say That Or Did You Calculate?

If you arrived at a person's date of birth from a date of death and an age at date of death then the resulting date of birth should be indicated as one that was calculated, not one the record actually stated. There are two reasons for this--1) never indicate a record says something it didn't (the birth date was not actually written on the record) and 2) who ever calculated the age might have done so incorrectly before it was written on the record or put on the stone.

Genealogists often use "Cal" for such calculated dates and your source for that calculated date should indicate the document that provided the specific age and the date the person was that age.