I know my parents’ ages, my husband’s parents’ birthdays and ages, and my grandparents’ birthdays and ages (except the exact birth date of the grandfather who died before I was born). My husband doesn’t know how old his parents are. We get together for birthdays but don’t really make a big deal out of them.
Mom’s fifty six and dad’s sixty five.
We celebrate every year with a nice gift and a nice dinner. Every 5 years it’s a bigger deal.
Yup both are in their mid 40’s.
I thought I was the only person to do that. My birthday is in June. Somehow that gets me more used to it.
I do. I also know how old their mothers are.
I sometimes have to take a moment to think on it, but I do know.
Mom 64
Dad 61
Sister 36
Me 39
Do I win anything? 
I know their birth dates. I don’t have their ages at immediate recall, but I can subtract.
I don’t think I’ve ever known without looking up my biological father’s exact age.
I know my mother’s birthdate. Is that strange? It’s not like it changes.
Who the hell doesn’t know how old their parents are? Mine are both deceased, but I always knew their ages and their birthdays. And now I know the dates of their death too.
I know their birthdays and my dad’s birth year, so I extrapolate from that. My mother is two years younger than him. Like some others above, I usually have to use my own birth year to calculate my own age, as the years tend to rush by faster as I get older, and sometimes I can’t keep up.
I know my older sister’s age because her birthday is a month before mine but she is two years older. My younger siblings? I know their birthdays but the years are a little fuzzy. I can narrow it down with some thought.
My mom is almost exactly 20 years older than I - she was born on Jan 7 and I was on Jan 23. Dad was born 4 years before she, altho he died 9 years ago. My father in law was born a month after my dad, and I only remember my MIL’s b-day because she graduated high school, turned 18 and got married all in the same week.
I’m good at remembering trivia, but important stuff, less so…
Dad 77
Mom 72
Bro 54
Sis 51
SIL 53
BIL 56???
Niece 30
Niece 27
Nephew 25
Niece 22
Niece 19
Great nephew 4
Great niece Uh… days away from 2
Who doesn’t know this right off the bat?
I know how old my surviving parent is, how old Dad would be if he was alive, how old my surviving grandmother is, and how old her recently-dead husband would be. For the other two grandparents I need to do some addition and substraction (I know when they died and how old they were at the time).
I know how old my mom & dad are, but sometimes I have to pause and do the math in my head to calculate from their birth years.
Dad’s DOB has been his briefcase combination for nearly 40 years, not that he’s needed it much in the fifteen that he’s been retired.
Yes it does because I know the months they were born in, so I know if they’ve turned yet or not. It goes first my dad in July, then my mom in November, then me in February.
I think I’m the opposite of the OP. A decade or so ago. I might have said I had a general idea but couldn’t be bothered to keep track of the exact number. But ever since my Dad’s cancer diagnosis I have been acutely aware of both their ages.
General idea until this year, when they both turned 80 and we had parties.
Of course I know how old my parents are, but my mother did try to play coy by describing herself as “21+” when I was a little kid. I asked her what that meant, and she said “A little bit older than 21.”
That ended when I told my kindergarten teacher that my mother was 22 
Mine are both at round numbers now (80 and 70) and we did a big to do for their birthdays, so I know right now. Sometimes I have to do the math in my head otherwise, but I know within a few years.