The real problem is that while the 50 year old has already had 30 years more learning than the 20 year old, the 50 year old probably doesn't know who the Kardashians are. How can you not know who the Kardashians are? What's wrong with you?
My exact experience.
I know it's just a throw-away example, but I'd like to point out "Keeping up with the Kardashians" has been on TV continuously since 2007. The more prominent Kardasihan sisters themselves are all 34-36 years old.
I don't think anyone in their 50s really would have a hard time relating to someone in their mid-30s, nor be completely flummoxed by a TV show that's been available for 10 years.
More to the point--pop culture is popular culture and seeps its way through all age groups. A better example would be a music artist that's popular only with teenagers or some niche group. I couldn't name a single artist popular with teens/tweens now.
You understand that you are unaware of the younger generation's pop culture (pop music is as much part of pop culture as TV is), but you don't understand how people of my generation can be unaware of your generation's pop culture.
I'd posit that generations can't have their own unique 'pop culture'. If it's only popular to people born within 10 years of you, then it's not popular. By my measure a lot of 'pop artists' aren't really popular because even appealing to 100% of tweens in the USA, really means you've captured 3% of the total general population.