Jason Kottke writes that "comparing my distorted recall of childhood favorites to the oldies of the time jogs my memory in unpleasant ways."
For example:When I was a kid, my mother's record collection (Paul Anka, Bobby Vinton, Bobby Vee) seemed horribly dated, but it was no less contemporary than, say, Nirvana is today. The effect is exaggerated in my case, because my musical tastes have always been a little out-of-date. I've been introducing one of my nieces to the works of Bob Dylan. His first album was released in 1962, 28 years before her birth. That's the equivalent of someone introducing me to Glenn Miller's "Chattanooga Choo Choo" back in 1987.
Listening to Michael Jackson's Thriller today is equivalent to listening to Elvis Presley's first album (1956) at the time of Thriller's release in 1982.
Let's apply Kottke's notion of "timeline twins" to genealogy. On 7 July 1997, I was exactly as old as my father was when I was born. Another way of looking at it is, on that date I was exactly half my father's age. I will always be closer in age to my father than to any child born since that date.
Here's a little widget that will calculate when a child reaches the age his/her parent was when he/she was born: