being normal, knowing movies, books and normal things?

What is the quickest way to know movies that are cross-generation ? And books and interests of a group that is 10-20 years older than me ? I am awfully dumb when I stand among them !!

What are some of the books that these people might find as most obvious books? (like 50 shades of gray for instance), who are the most wanted actors and actresses, what hobbies do they like ?