I've noticed that there seems to be a time anchoring that happens around your formative years which is why most people think 10 years ago = high school || college age - 10.
I was speaking to someone at a party and for some reasons the topic of 9/11 came up and they mentioned they weren't born when it happened so I just stopped talking to them.
While the phenomenon he explains does exist, it is an incorrect explanation for the feeling described in your title. This video is amazing, and I suggest watching all of it or just jumping to 10:50 to see your explanation:
P.S.: I was born in 2000, but ffs what's up with these short format videos of people talking really fast and shoving incorrect info down your throat? I just can't watch these, nor can I understand what they are saying.
For a second I thought you looked up their birthdays and this was literally about the fact that Tobey Maguire was 23-years-old playing a college kid and only one year younger than this actor playing a middle-aged dad and it was a funny haha moment about Hollywood casting and age discrepancy between actors and the characters they play.
Then I did some more thinking and remembered that Spider-Man 2 came out in 2004 and I am an idiot.
BTW Tobey Maguire was born in 1975 and the other actor's name is Peter Allas and I couldn't find his birthday.
Seeing this meme has set me on a Mr Sunday Movies binge. I'd been off them for a bit since they were mostly covering things I wanted to see and didn't want spoiled