Question

Why doesn’t Patrick Douglas know his true birthdate or age

Answer 1

It could be that he is adopted. Hope this helps.

Answer 2

I think you must be thinking of Frederick Douglass, the abolitionist who escaped from slavery.

He was born into slavery in Talbot County, Maryland, circa 1818. He chose his birthday to be February 14th. Official vital records for enslaved people were not often kept or maintained. Documentary evidence is usually based on records from the sale of enslaved people.