I know what you mean.
I memorized both of my parents' phone numbers when I was still a kid.
I also know the birth-dates of every single one of my family members: Mum, Dad, My brother, My sister, my little brother and me. And also my aunt's birthday~!! And not to mention, my cousin's birthday (let's call her cousin 1) and the birth dates of cousin 2, cousin 3 and cousin 4 on the other side of the family.
I learnt all that since when I was younger than 12... except my aunt's birthday. Now that I worked out the year she was born, I know her birthdate too
EDIT: Wait, before I forget... Many adults say that I'm very observant. I think that means that I notice things very well?
I think it sort of helps when you are born on a National Day of a country and are named for a symbol of that specific country, I guess.