There’s a potential gray area here.
Information is considered to be primary is the informant reasonably had first hand knowledge of the information. It is worth noting that all memory can be fallible. 
I know my precise date of birth not because I remember the actual day. I remember my birthday because I’ve been told it numerous times and it’s on my birth certificate. I cannot provide primary information regarding my date of birth because I do not have personal memory of being born on that day. This does not mean the date is wrong–just that I cannot provide that primary information myself.
Can I provide primary information on my approximate age?
Sure. If I stop and think, I can remember being in the third grade during the US presidential election where the “peanut president won.” I remember it was third grade because it was when I was in Mrs. Putman’s class and she was my third grade teacher. Assuming that my memory is correct, I can fairly closely approximate my age from something that I myself remember. I also remember the year I graduated high school as well. Usually a person can “remember” their approximate age if they stop to remember ages they were at certain events, etc. That’s different from claiming to remember your exact date of birth.
Classification of information as primary or secondary merely indicates our perception of how the informant came to know something that they claim to know.
Whether they are correct is another matter entirely.
6 Responses
I found my uncle’s birth registered in SEPT of the year he was born but he always celebrated in October…There were others registere ( haanwritten, contemporaneously) after his, still in Sept. Apparently he just celebrate it wrong.
As an example, my grandfather always teasingly gave me a bad time because my daughter was born the day after his birthday. After he passed away, his birth certificate was needed for something. That is how we discovered that she was born on his birthday, and he wasn’t there for me to tease him and get even. His parents told him that his birthday was December 10 instead of the 11, so he celebrated the wrong day his whole life.
Wouldn’t it be just as likely that “they” put the wrong day on the Registration form (Maybe the day they were filling it out?) Parents (at least mothers) would generally have it right!!!
Even someone who has first hand knowledge can get a date wrong–often for a variety of reasons 😉
After the death of the father of my step-father, he went to clear out the house and came across his birth certificate. Pop was surprised to discover he was two or three years older than he thought he was! I found that astounding.
Grandma celebrated, knew and was proud she shared a birthday with George Washington. In adulthood she had to get a copy of her birth record & was incensed to learn her father had reported the date as the 24th of Feb. One more sin of the father.