So my girlfriend is 3 years younger than me. Not a very large difference, however, in the world of nostalgia and pop culture... that can be a lifetime.
Not to mention there are a few things that I love but she does not (sports, scifi, superheroes, cartoons, action movies, etc.). Some would say she's more mature because she is less aware of some of these subjects. And in fact, she has a pretty good knowledge base when it comes to entertainment. I'm just here to list the gaps.