I think what this question implies is that young females are hesitant about entering erotic relationships and about taking charge of the relationship, whereas young men are not. If gender roles is defined by who advances the relationship, then Juliet would definitely be the driving force.
On the balcony, Juliet expresses her passion for Romeo, whom she has just met. Romeo, unbeknownst to her, overhears her avowal of love. Other than Romeo's freedom to move about on his own at night, this doesn't necessarily involve a gender reversal. However, when Juliet realizes she cannot play coy since Romeo has heard her, she actually proposes to him. This might seem forward for a young woman, but she acknowledges that it would be pointless to pretend she hadn't already expressed her feelings.
From this point on, Romeo is slower and more passive in the relationship, while Juliet arranges for the marriage, the consummation of the marriage, and the secret plot to drink poison and return to Romeo.
She is clearly the character who changes the most, grows the most, and most expresses a complex and strong self. This may be an issue of gender reversal, but I think that in talking about Shakespeare, we should remember that he is about to write his romantic comedies, and Portia, Beatrice, and Rosalind are equally strong female characters. The greater difference is that they appear in comedies rather than tragedies. In comedies, female independence and strength are assets rather than a sign of rashness, as they seem to be here.