The first characteristic that can be associated with Romeo is that he is impetuous and rushes into things way too quickly without thinking about the actions that he is taking or the outcomes that might occur from those actions. Romeo can also be characterized as a romantic. Unlike his friend Mercutio, Romeo wants to all that he can to woo the girl that he is in love with. An example of this is the way that he speaks with Juliet the first time that he meets her. A third characteristic of Romeo is his immaturity. Romeo wants to act as though he is older than he actually is (for example, getting married before he is ready) but in trying to act older, he is bringing out his immature side.
Juliet shares two characteristics with Romeo. Like Romeo, Juliet is also impetuous and immature for exactly the same reasons as Romeo – she, too, rushes into things too quickly and acts immature. A third characteristic of Juliet is her strength and conviction. Juliet it determined to never marry Paris; and, although against her father’s better judgment, she is able to make this happen.
It's true R&J both come from "affluent families, but I'd like to point out that these families are not royalty, but merchants. Why is this important? Aristotle's Poetics says that tragic characters must come from families of kings and queens (or words to the same effect). If you think of it, Hamlet is a prince, Macbeth is a king, etc. Some people think that this is among several "definitions" or "rules" of tragic plays. I think it is much more likely that he is describing plays written for two festivals in which playwrights competed for prizes, and that those plays had certain rules.
I think Romeo and Juliet is a tragedy. Scholars, however, usually call it a "domestic tragedy," that is one which describes the suffering of characters who are not members of ruling families. If you think about it, Othello is also such a play. There are three or four other plays which survive from Shakespeare's time which are more like R&J and Othello than like Hamlet or King Lear.
I think the "tragedy" is no less sad or effecting in these plays. If you think about it, Death of a Salesman is also such a play. Miller devotes a lot of speeches comparing Willie Loman to great tragedies of the past. I think a dandy paper could be written, after a good bit of research, about this whole concept.
Both characters are young, both are from affluent families, and both are madly in love. The first thing we notice about these characters is their family life: Both the Capulets and Montagues are upper-echelon families within their community. Their affairs are public knowledge, as they are seen as examples of what life should be like during this era.
Another fact about both of these characters is that they are young -- in fact, they both are considered teenagers. The two are madly in love with one another, a shared emotion. These similarities bond the characters of Romeo and Juliet within the plot of the play itself.
We're doing something similar in my class. My teacher gave examples like "the was they express their love, the courage they may or may not show in the face of difficulties, or the types of relationships they have with friends and family". Hope this was helpful!