Yeah, you'd think. But when I started dating my wife my mother in-law was 38. They were having a birthday cake for my father in-law. I just asked "What year were you born?" and he said 1927. I said that's the same year my mom was born, so that makes you 51 today. My mother in-law turned white as a sheet and panically blurted out "YOU CAN'T TELL MY PARENTS!!!"
I asked "They don't know??? How long have you been married???"



Man! My dad's 8 years older than my mom and his dad is 8 years older than his mom. I couldn't understand why there'd be a problem but swore to never mention anything.
So my mother in-law proceeds to tells me that her parents knew he was older, but no where near the actual difference. They didn't like him and didn't want her to marry him. So she ran away from home (went to her girl friend's house) and stayed there for several weeks until her parents relented.
My father in-law was an extremely good husband, father, and son in-law. Ever since I met him he'd mow his in-law's lawn every week, their elderly neighbors lawns, shovel their snow, clean their gutters, etc... good provider and about the best work/play ethics I'd ever seen in a human. I have no idea why they didn't like him other than they were Hungarian and he was Polish, and something happened in the old country before either one of them were born and it was a grudge two generations and an ocean away.
Heck, my father in-law even moved his mother in-law into their home after her husband passed and kept care of her for a few years until her dementia was too much to handle.
It was nice to see him get one over on his in-laws.