In the 1996 film, how does Baz Lurhman tackle the young ages of Romeo and Juliet?

Well, in this updated film version of the play
Romeo and Juliet, Baz Lurhman does what Franco Zeffirelli did
before him -- he cast two actors very close in age to the characters of Romeo and
Juliet.

The youthful acting work of these teenage actors
stands in pretty sharp contrast to the more mature work of most actors cast in
theatrical stagings of the play.  Both parts are rigorous and demanding for any stage
performer, and the actors usually cast to play them onstage are in their early to mid
twenties.  Sometimes, actors in their thirties have played these
roles!

In Shakespeare's time, the roles would, most
probably, also have been played by teenagers, but both parts would have been played by
teenage boys.  So, both Zeffirelli and Lurhman are closer to the original staging with
their casting choices.

Shakespeare created two very unique
characters in Romeo and Juliet, in that it is Juliet who speaks and behaves as a young
male lead character should (speaking directly and taking courageous action) and it is
Romeo who speaks in flowery, romantic verse and is much more reluctant to initiate
action.

So, the main choice Lurhman makes in his film
Romeo + Juliet is to cast young actors in the parts.  In this way,
the youthful impulses of Leonardo DiCaprio and Claire Danes can shine through these
teenage star-crossed lovers.