What is the generation gap in Romeo and Juliet?

First, let's examine what a generation gap means. Our contemporary definition of a generation gap refers to the differences in opinions or outlooks between people of different generations or the time period in which one is born and lives. Since we can't apply the modern labels of generations (for example, the terms "Millennials" or "Baby Boomers") to Romeo and Juliet, we must simply re-frame this question within the context of the two broader rivaling factions in this play: the matriarchs and patriarchs of the Capulet and Montague families versus the young people of the Capulet and Montague families. 

There are several instances in which a "generation gap" can help explain the conflicts that occur here. The first instance would be that of the longstanding hatred between the Montagues and Capulets. We are never explicitly told WHY these two families despise each other; we simply know this feud has been an age-old "tradition" of sorts, one passed down from parent to offspring with little thought as to whether or not it is necessary or practical to maintain. The adults of Romeo and Juliet—Lord and Lady Capulet and Lord and Lady Montague—are hellbent on keeping this hostile atmosphere alive. The young people—Romeo and Juliet—are far more relaxed in their attitudes, departing so far from their parents' outlooks that they actually fall in love with one another. Perhaps Juliet articulates this radical attitude best in her iconic speech from Act Two: 

What's in a name? that which we call a rose

By any other name would smell as sweet...

Juliet is essentially arguing that her parents' rivalry with the Montagues is ridiculous and that a human should be judged on the value of his or her character rather than the merit of his or her name—a very modern idea indeed!

We can also see evidence of a generation gap in the pressure the Capulets put on their very young daughter to marry. Juliet Capulet is only 13 years old, and yet her father holds staunchly to the belief that he must marry her off—with or without her consent—as soon as possible. Juliet's resistance to marriage is more evidence of the modernity of her relationship ideals compared to those of her parents; this refusal to obey the house rules was revolutionary considering the emphasis placed on subservience in women at the time.